Aromatase Inhibitor Effectiveness on Height Augmentation: Optimizing Letrozole Therapy for Height Gain in Short-Statured Boys

Aromatase Inhibitor Effectiveness on Height Augmentation: Optimizing Letrozole Therapy for Height Gain in Short-Statured Boys | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Research Article Aromatase Inhibitor Effectiveness on Height Augmentation: Optimizing Letrozole Therapy for Height Gain in Short-Statured Boys Davoud Amirkashani, Ghazal Tavakoli, Amir Ghanbari, Kiana Orangi, and 1 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-7103844/v1 This work is licensed under a CC BY 4.0 License Status: Posted Version 1 posted You are reading this latest preprint version Abstract Background Aromatase inhibitors (AIs) such as letrozole (Lz) have proposed to increase final adult height by delaying epiphyseal closure through reducing estrogen synthesis, but optimal timing for initiation and duration of treatment remains unclear. Objective To evaluate the effect of Lz, with or without recombinant human growth hormone (rhGH), on final adult height (FAH) and to identify treatment duration and bone age thresholds that maximize clinical responsiveness. Methods A retrospective cohort study of 40 boys with bone age of 12–16 years with the diagnosis of idiopathic short stature (ISS) or growth hormone deficiency (GHD) and no prior history of growth-modulating therapy followed to their FAH. They have been treated with Lz (2.5 mg/day) for 1 to 2.5 years. Nine received Lz as monotherapy and 31 received Lz + rhGH. Results Both letrozole monotherapy and combination therapy demonstrated significant increases in FAH versus predicted adult height (PAH) with the height augmentation of 2.30 ± 1.24 cm and 4.40 ± 2.51 cm, respectively (p < 0.001). In the Lz + rhGH group, height augmentation positively correlated with treatment duration up to a 21-month breakpoint (ρ = 0.703, p < 0.001), while beyond that point, the effectiveness decreased significantly. Notably, height augmentation negatively correlated with baseline bone age (ρ = − 0.367, p = 0.0425). Patients treated at or below a bone age of 14.5 years gained 5.15 cm compared to 2.58 cm in older boys (p = 0.018). Conclusions Administering Lz with GH after a bone age of 14.5 years showed a significant decrease in height augmentation. Moreover, extending Lz therapy up to 21 months enhances this gain, while benefits appear to decrease significantly beyond that point. Early initiation and careful optimization of treatment duration maximize efficacy and minimize the risk of overtreatment and adverse effects. Letrozole Aromatase Inhibitors Growth hormone Short-stature Figures Figure 1 Figure 2 Figure 3 INTRODUCTION Short stature is a common reason for referral to pediatric endocrinology clinics and it can cause significant psychological and social stress for both parents and children(1). The most common etiological factors of short stature are Constitutional Growth Delay (CGD), Idiopathic Short Stature (ISS), malnutrition and Growth Hormone Deficiency (GHD) and is a condition in which the height of the individual is more than 2 SD below the corresponding mean height for a given age, sex and population(2, 3). Recombinant human growth hormone (rhGH) is a widely used treatment for short stature; however, it is an expensive medication and typically offers only modest improvements in final height for children who are not growth hormone deficient(1, 4, 5). Notably, approximately 60–80% of children with short stature are classified as having idiopathic short stature (ISS), meaning that no underlying pathology or alternative diagnosis can be identified (1, 6). Aromatase inhibitors (AIs) such as letrozole and anastrozole; have been proposed as an alternative treatment of short stature individually or in combination with rhGH to augment height in male with or without classic GHD (7–9). AIs suppress the conversion of testosterone to estrone and estradiol (E2), the hormone that regulates bone maturation and epiphyseal plate closure which lead to cessions of growth during puberty. In theory, a reduction in estrogen production during the pubertal growth period would permit a longer interval for growth and result in an increase in final adult height. Anastrozole and letrozole are third-generation nonsteroidal AIs that bind to the active site of the aromatase enzyme and block estrogen formation and lead to a significant increase in predicted adult height (PAH) as well as an increased height standard deviation score (HtSDS) for bone age(1, 8, 10). However, the available data on the efficacy of aromatase inhibitor (AI) therapy are limited and sometimes controversial(11, 12). It remains unclear at what specific bone age or under which clinical conditions AI therapy is most effective. This lack of clarity complicates the decision-making process for healthcare providers and emphasizes the need for further research to determine the optimal timing and indicators for implementing AI therapy. This article aims to explore the effects of letrozole on final adult height, ascertaining the relationship between its use and changes in growth patterns. Additionally, we will investigate the correlation between timing of letrozole administration concerning patients' bone age with the predicted and actual adult height. By examining the letrozole's administration impact on bone age and height outcomes, we aim to enhance our understanding of its utility in clinical practice and treatment strategies for optimizing adult height among affected individuals. METHODS Study Design and Participants This study was designed as a retrospective cohort analysis of mid-and late-pubertal male pediatric patients with short stature who were referred to our endocrinology clinic at Ali Asghar Children's Hospital. We reviewed medical records for male patients which a pediatric endocrinologist had confirmed the therapeutic benefit of letrozole (Lz) and started treatment with Lz, meeting inclusion criteria, including chronological age over 11 years, bone age above or equal to 12 years but below or equal to 16 years, diagnosis of growth hormone deficiency (GHD) or idiopathic short stature (ISS) which is defined as height more than 2 standard deviations below the mean height of their similar age and sex group(3). We also include patients which their baseline and follow-up data were available with no missing data, and patients that had no prior treatment with growth hormones, letrozole, or other aromatase inhibitors. We excluded patients with endocrine or genetic disorders, other comorbidities, previous medical treatment for short stature or missing data. Letrozole therapy was initiated based on individual assessment of growth potential and bone age by a pediatric endocrinologist. The study population comprised of 40 boys with chronological age over 11 years old with ISS or GHD who were treated with Lz (2.5 mg/day) for a mean duration of 21 months, either as monotherapy or in combination with growth hormone. Nine boys received Lz as monotherapy, while 31 received combined Lz with growth hormone (GH). Lz initiation was individualized based on bone age, growth changes, clinical features, and clinical benefit assessment during follow-ups by the pediatric endocrinologist. Recombinant human growth hormone was given 0.035 mg/kg daily, using the brand CinnaTropin. Measurement & Data Collection Relevant clinical and laboratory data were extracted from patient records from the endocrinology clinic at Ali Asghar Children's Hospital, including chronological age (CA), bone age assessment using graphic image of the left hand and wrist according to the Greulich and Pyle method, Tanner stage evaluated by comprehensive physical examination performed by an endocrinologist, mid-parental height (MPH), baseline height were measured by standard weight scale, predicted adult height (PAH), which was calculated using established methods (Bayley-Pinneau technique) by an endocrinologist, final adult height (FAH) and duration of letrozole treatment(13, 14). Every 3 months in the pediatric endocrine clinic of Ali Asghar Children's Hospital, examination was performed by the same physician (D.A.) throughout the study. Patients were followed up to reaching FAH characterized as bone age equal or greater than 17 years. Statistical Analysis Data analysis was performed using Python (version 3.12). Continuous variables were reported as mean ± standard deviation and categorical variables were reported as percentages. Comparisons between baseline and follow-up measurements were made using paired t-tests or non-parametric alternatives, such as Wilcoxon signed-rank tests. Spearman correlation coefficients were calculated to assess the relationship between baseline chronological age, bone age and duration of Lz treatment with the final adult height (FAH) and Height augmentation percentage. Height augmentation percentage was calculated with the following formula: Height augmentation (%) = (FAH – PAH) / PAH Additionally, scatter plots, bar plots and box plots were performed to visualize data distributions and investigate the factors influencing height outcomes. A p-value of less than 0.05 was considered statistically significant. Ethical Considerations This study was conducted in accordance with the ethical principles outlined in the Declaration of Helsinki. Ethical approval was obtained from the Ethics Committee of Iran University of Medical Sciences (IR.IUMS.FMD.REC.1404.194). RESULTS The study population comprised of 40 mid- and late-pubertal boys with a chronological age ranging from 11.5 to 15.5 years. 31 received both Lz and GH, while 9 received Lz as monotherapy (Table 1 ). The mean age of the total population were 13.6 ± 1.15 years at the initiation of treatment. The mean height at baseline was 150.4 ± 5.6 cm, and the mean bone age was 14.2 ± 0.7 years. All patients were treated with letrozole ranging from 1 to 2.5 years for an average duration of 1.8 ± 0.4 years. Sexual maturation was assessed using Tanner staging and from the 40 participants, 21 (52.5%) were classified as Tanner stage IV, 18 (45%) as stage III, and 1 (2.5%) as stage II, with the median of stage III. Table 1 Anthropometrics characteristics of the 40 adolescent males receiving Letrozole (Lz) + Growth hormone (GH) or Lz as monotherapy . Values are expressed as mean ± SD. MPH: Mid parenteral height, SMR: Sexual maturation rate. Characteristics Lz + GH (n = 31) Lz (n = 9) Chronological Age 13.52 ± 1.07 13.86 ± 1.43 Bone Age 14.13 ± 0.71 14.44 ± 0.81 Initial Height 149.91 ± 5.36 151.92 ± 6.55 MPH 169.26 ± 3.71 166.78 ± 3.38 PAH 161.67 ± 1.34 163.26 ± 0.85 SMR 3 (median) 3 (median) Months with Lz 21.68 ± 4.94 19.33 ± 5.43 Months with GH 15.48 ± 2.46 - Paired t-tests revealed that both Lz monotherapy and Lz combined with GH produced a highly significant increase in final adult height relative to predicted adult height (p < 0.001), validating letrozole effect on the height augmentation with or without GH (Table 2 ). A comparison between Lz and Lz + GH groups also identified greater height increment in the Lz + GH group (4.4cm, 2.3 cm respectively, p = 0.0019) suggesting that Lz + GH might be a better treatment strategy. Spearman test was also conducted to investigate the correlation between duration of Lz therapy in Lz + GH group and heigh augmentation (cm). A positive correlation was found between the months on Lz therapy and height augmentation (Spearman ρ = 0.703, p < 0.001). This implies that longer treatment duration is associated with increase in height gains, while piecewise linear regression revealed a breakpoint at 21 months of letrozole treatment. Height augmentation increased up to 21 months, after which the rate of improvement plateaued. This suggests that the main therapeutic benefits are achieved within the first 21 months of therapy (Fig. 2 -A). Spearman correlation test was conducted to assess the relationship between height augmentation with the bone age and chronological age which the treatment with Lz + GH started. A significant negative correlation was observed between height augmentation and either bone age (Spearman ρ = -0.367, p-value: 0.0425) or chronological age (Spearman ρ = -0.559, p-value: 0.001). This indicates that as bone age and chronological age increases, the effectiveness of Lz + GH in height enhancement decreases, reinforcing the importance of early intervention. A segmented regression was conducted to investigate a critical threshold in the relationship between bone age and height augmentation in Lz + GH receiving group. This analysis identified a breakpoint at a bone age of 174 months (~ 14.5 years). Prior to this threshold, height augmentation tended to increase with bone age; however, around 14 years a decline in treatment response was observed suggesting a bone age estimated around 14.5 years threshold for effective letrozole therapy indicating reduced efficacy of letrozole at more advanced skeletal maturity (Fig. 2 -B). Moreover, a t-test was conducted by categorizing patients into two groups based on the bone age (bone age ≤ 14.5 years and bone age > 14.5 years). Height augmentation was calculated as the difference between final adult height and predicted adult height. Results showed a significantly greater height augmentation in the 14.5 years and younger group (5.15 cm) compared to those older than 14.5 years (2.58 cm). A t-test confirmed that this difference was statistically significant (t = 2.68, p = 0.018), suggesting that earlier initiation of letrozole therapy along with GH (bone age ≤ 14.5 years) is associated with an increase in final adult height (Fig. 3 ). We also conducted an independent t-test following categorizing patients into two groups of Tanner stage IV and another group of Tanner stage III and II. The results suggested no significant difference in height augmentation between the two groups (t:1.50, p: 0.14). Table 2 Comparison of predicted adult height (PAH) versus final adult height (FAH) , the absolute and percentage height gains, and paired t-test results for boys receiving letrozole plus growth hormone (Lz + GH) or letrozole monotherapy (Lz). Values are reported mean ± SD; ***p < 0.001 indicates highly significant FAH increase over PAH. PAH (cm) FAH (cm) FAH-PAH (cm) Height augmentation (%) p Lz + GH (n = 31) 161.67 ± 1.34 166.07 ± 1.90 4.40 ± 2.51 2.73% < 0.001 (***) Lz (n = 9) 163.26 ± 0.85 165.56 ± 1.43 2.30 ± 1.24 1.41% < 0.001(***) Discussion Utilizing the best strategies to enhance final height in short stature boys is a substantial challenge, due to narrow therapeutic time during puberty and the psychosocial impact of short stature. Moreover, evidence regarding final adult height outcomes following aromatase inhibitor therapy remains limited and inconsistent. We conducted a retrospective analysis of 40 mid and late-pubertal boys with ISS or GHD followed to their final adult height, evaluating the effect of Lz on FAH, identifying treatment duration and bone age thresholds associated with optimal clinical response. The timing of therapy initiation emerged as a critical factor in our study. Also, side effects such as increased facial hair may cause social challenges in younger boys, supporting the need to better define the optimal age window for letrozole therapy. We found that boys who began letrozole at a bone age above 14.5 years had significantly lower height augmentation compared to those aged 14.5 years or younger (2.58 cm and 5.15 cm, respectively). This highlights the golden time of starting Lz and the limited residual growth potential once the epiphyses are nearing closure. Varimo et al.(15) initiated Lz in pre- to early-puberty, also implied that too early intervention might not cause significant height gain and highlight the possible optimal treatment window. Our findings are aligned with the general principle that late-puberty offers less time for height gain and the benefits of Lz treatment begin to diminish in this state(16). To conclude, even though our study showed some benefits can still be attained after the bone age of 14.5 years, this improvement is modest compared to earlier intervention. Further research is needed to better define the optimal timing for treatment initiation. Therapy duration is equally important, as height gains had positive correlation with letrozole treatment duration, up to the point of 21 months, after which incremental benefits plateaued. Extending beyond two years may confer only marginal benefit but make them prone to side effects, also discontinuing too soon may result in the loss of a part of the PAH gain. Our study is among the few studies to evaluate the relationship between either letrozole duration or initiation timing and final height gain, providing new insight into the optimal treatment window. Interestingly, we did not observe any significant difference in efficacy between Tanner stage III and Tanner stage IV at treatment start. This finding is reassuring, as it indicates that boys presenting later in puberty can still benefit from AI therapy while bone age and growth plates suggest possible growth potential. This also highlights the importance of bone age relative to the tanner stage for clinical decision making. Our findings demonstrated that letrozole therapy with or without GH produced clinically meaningful improvements in height outcomes. FAH significantly exceeded the initial PAH in the treated boys, indicating that monotherapy is effective in promoting height gain, consistent with findings from several previous studies (10, 17–20). Gavan et al.(18) evaluated the 27 AI treated mid-pubertal boys and reported Lz monotherapy effectively increased height by delaying the bone maturation and making the pubertal growth phase longer. They also pointed at the height gain of 3.8 ± 3.5 cm in treatment group compared to only 0.3 ± 5.0 cm in untreated controls. Similarly, Rohani et al.(10) reported a significant final height gain of 1.9 cm in CDGP boys treated with Lz. Aligned with the previous studies following patients to their FAH, we found letrozole monotherapy resulted in a height gain of 2.30 ± 1.24 cm, reflecting a significant increase relative to PAH. In a study by Salehpour et al.(17), 31 of CDGP boys with the bone age of 12.18 ± 1.1 treated with Lz for two years. Their findings, while similar in trend, reported a significant increase in PAH (6.1 ± 1.9 cm, p < 0.01); however, unlike our study, they did not report outcomes to FAH. In contrast, our study following patients to their FAH and demonstrated significant increase in FAH relative to PAH. The greater height gain reported by Salehpour et al. may be attributed to differences of study design and methodologies, as they recalculate PAH after the end of treatment duration, while we followed our patients to their FAH. Additionally, it might be due to initial bone age difference of them having younger population (12.18 ± 1.1 years) compared to our study (14.44 ± 0.81 years). Our findings are in contrast with several studies, which found no effect of AI monotherapy on height gain in boys with short PAH(8, 15, 16, 21–23). This controversy might be due to study design differences. Our study comprised of homogeneous group of mid- to late-pubertal male population followed up to achieve FAH, whereas most of the earlier studies had smaller sample sizes and assessed only changes in PAH without long-term follow-up to FAH. Varimo et al.(15) also followed patients to their final height but reported no significant height gain in the Lz treatment group, while their sample size was smaller(n = 10) and they consisted of pre- to early-pubertal boys with the mean bone age of 9.2 ± 2.6, while our study focused mainly on mid- to late-pubertal boys with the mean bone age of 14.44 ± 0.81 years. This discrepancy suggests that Lz may be less effective in younger bone ages but a more applicable treatment in more advanced bone ages, although future studies are needed to clarify the age range in which letrozole is the most effective. We found that the combination of rhGH and Lz led to a significant increase in FAH, with a gain of 4.40 ± 2.51 cm above the PAH, highlighting rhGH + Lz as a promising therapeutic strategy for enhancing height outcomes. We also observed greater height increment in the rhGH + Lz group (4.40 ± 2.51cm) in comparison with the Lz alone (2.30 ± 1.24). Similarly, Maures et al.(19) and several other studies suggested AIs particularly showed better results in combination with GH compared to Lz alone(15, 21, 22). A 2024 meta-analysis confirmed that adding AIs to rhGH leads to higher growth velocity and PAH compared to rhGH as monotherapy, (24). Consistent with the meta-analysis, Zhang et al.(25) concluded rhGH + Lz combination showed better height outcome than the rhGh + GnRH group. These findings collectively underscore rhGH + Lz as a proven superior treatment strategy for maximizing height outcomes in short-statured children. This study has several limitations. The modest sample size and retrospective design may cause a selection bias. Choosing the treatment strategy was not randomized, and although we compared final height to each patient's own PAH, confounding factors may remain. Additionally, this study did not assess the safety or side effects, thus further larger prospective trials are needed to evaluate these outcomes. However, this study has important strengths. It is among the few to follow patients to their final adult height, allowing for a more definitive and precise evaluation of treatment efficacy. Moreover, it is the first study to investigate the influence of initial bone ages on letrozole responsiveness, suggesting that the treatment may be more effective at certain bone ages. Conclusion In summary, we observed that letrozole, both alone and in combination with growth hormone, yields a modest but significant increase in final adult height over the predicted adult height at baseline, with combination therapy producing the better outcomes. Height augmentation positively correlates with letrozole duration up to about 21 months and declines after the bone age of 14.5 years, underscoring the importance of earlier intervention and avoiding overtreatment. Given the lack of comparable research, larger prospective trials are needed to refine optimal age and duration thresholds and to avoid overtreatment and side effects. Declarations Acknowledgments Funding and Assistance The authors received no specific funding for this research. Conflict of Interest The authors declare no conflicts of interest related to this work. Author Contributions All authors contributed to the study design and methods. D.A. collected the data, while G.T. and A.G. wrote the first draft of the manuscript. G.T. performed the statistical analysis and generated the figures for the result section. K.O. reviewed the initial manuscript and designed the graphical abstract. D.A. critically reviewed and edited the manuscript and provided final approval of the manuscript. All authors commented on and revised the manuscript. Prior Presentation This study has not been previously presented at an annual meeting or other conference. Ethical Approval This study was conducted in accordance with the ethical principles outlined in the Declaration of Helsinki. Ethical approval was obtained from the Ethics Committee of Iran University of Medical Sciences (IR.IUMS.FMD.REC.1404.194). Consent to Publish All authors have read and approved the final manuscript and give their consent for publication. Data Availability Statement Data will be available due to reasonable requests from the corresponding author. References Zegarra W, Ranadive S, Toulan D, Neely EK. Anastrozole vs Letrozole to Augment Height in Pubertal Males With Idiopathic Short Stature: A 3-Year Randomized Trial. J Endocr Soc. 2024;8(10):bvae141. Sultan M, Afzal M, Qureshi SM, Aziz S, Lutfullah M, Khan SA, et al. Etiology of short stature in children. J Coll Physicians Surg Pak. 2008;18(8):493–7. Wit JM, Clayton PE, Rogol AD, Savage MO, Saenger PH, Cohen P. Idiopathic short stature: definition, epidemiology, and diagnostic evaluation. Growth Horm IGF Res. 2008;18(2):89–110. Mauras N, Attie KM, Reiter EO, Saenger P, Baptista J. High dose recombinant human growth hormone (GH) treatment of GH-deficient patients in puberty increases near-final height: a randomized, multicenter trial. Genentech, Inc., Cooperative Study Group. J Clin Endocrinol Metab. 2000;85(10):3653–60. Reiter EO. A brief review of the addition of gonadotropin-releasing hormone agonists (GnRH-Ag) to growth hormone (GH) treatment of children with idiopathic growth hormone deficiency: Previously published studies from America. Mol Cell Endocrinol. 2006;254-255:221–5. Cohen P, Rogol AD, Deal CL, Saenger P, Reiter EO, Ross JL, et al. Consensus statement on the diagnosis and treatment of children with idiopathic short stature: a summary of the Growth Hormone Research Society, the Lawson Wilkins Pediatric Endocrine Society, and the European Society for Paediatric Endocrinology Workshop. J Clin Endocrinol Metab. 2008;93(11):4210–7. Dunkel L. Update on the role of aromatase inhibitors in growth disorders. Horm Res. 2009;71 Suppl 1:57–63. Shams K, Cameo T, Fennoy I, Hassoun AA, Lerner SE, Aranoff GS, et al. Outcome analysis of aromatase inhibitor therapy to increase adult height in males with predicted short adult stature and/or rapid pubertal progress: a retrospective chart review. J Pediatr Endocrinol Metab. 2014;27(7-8):725–30. Varimo T, Huopio H, Kariola L, Tenhola S, Voutilainen R, Toppari J, et al. Letrozole versus testosterone for promotion of endogenous puberty in boys with constitutional delay of growth and puberty: a randomised controlled phase 3 trial. Lancet Child Adolesc Health. 2019;3(2):109–20. Rohani F, Asadi R, Mirboluk AA, Soheilipour F. Letrozole Effect on Final Height of Patients with Constitutional Delay of Growth and Puberty. Med Arch. 2019;73(5):307–10. Varimo T, Toiviainen-Salo S, Raivio T, Kerttula L, Dunkel L, Hero M. Letrozole Monotherapy in Pre- and Early-Pubertal Boys Does Not Increase Adult Height. Front Endocrinol (Lausanne). 2019;10:201. Geffner ME. Aromatase inhibitors to augment height: continued caution and study required. J Clin Res Pediatr Endocrinol. 2009;1(6):256–61. Bayley N, Pinneau SR. Tables for predicting adult height from skeletal age: revised for use with the Greulich-Pyle hand standards. J Pediatr. 1952;40(4):423–41. Greulich WW, Pyle SI. Radiographic atlas of skeletal development of the hand and wrist. The American Journal of the Medical Sciences. 1959;238(3):393. Varimo T, Toiviainen-Salo S, Raivio T, Kerttula L, Dunkel L, Hero M. Letrozole monotherapy in pre-and early-pubertal boys does not increase adult height. Frontiers in Endocrinology. 2019;10:201. Ferris JA, Geffner ME. Are aromatase inhibitors in boys with predicted short stature and/or rapidly advancing bone age effective and safe? J Pediatr Endocrinol Metab. 2017;30(3):311–7. Salehpour S, Alipour P, Razzaghy-Azar M, Ardeshirpour L, Shamshiri A, Monfared MF, et al. A double-blind, placebo-controlled comparison of letrozole to oxandrolone effects upon growth and puberty of children with constitutional delay of puberty and idiopathic short stature. Horm Res Paediatr. 2010;74(6):428–35. Yackobovitch-Gavan M, Tenenbaum A, Phillip M, Lazar L, Oron T. Aromatase-inhibitors Treatment Alone or with GH Increases Final Height in Short-Statured Pubertal Boys - Real-World Data. J Clin Endocrinol Metab. 2025. Mauras N, Ross JL, Gagliardi P, Yu YM, Hossain J, Permuy J, et al. Randomized Trial of Aromatase Inhibitors, Growth Hormone, or Combination in Pubertal Boys with Idiopathic, Short Stature. J Clin Endocrinol Metab. 2016;101(12):4984–93. Dutta D, Singla R, Surana V, Sharma M. Efficacy and Safety of Letrozole in the Management of Constitutional Delay in Growth and Puberty: A Systematic Review and Meta-analysis. J Clin Res Pediatr Endocrinol. 2022;14(2):131–44. Likki SR, Allen HF, Knee A, Tonyushkina KN. Use of letrozole to augment height outcome in pubertal boys: a retrospective chart review. J Pediatr Endocrinol Metab. 2022;35(10):1232–9. Pedrosa LF, de Oliveira JM, Thomé PRV, Kochi C, Damiani D, Longui CA. Height Increment and Laboratory Profile of Boys Treated With Aromatase Inhibitors With or Without Growth Hormone. Horm Metab Res. 2017;49(10):778–85. McGrath N, O'Grady MJ. Aromatase inhibitors for short stature in male children and adolescents. Cochrane Database Syst Rev. 2015;2015(10):Cd010888. Wang K, Ye F, Wang DY, Lai PJ, Zhang LQ. Aromatase inhibitors for short stature in male children and adolescents treated with growth hormone: a meta-analysis of randomized controlled trials. BMC Pediatr. 2024;24(1):813. Zhang Y, Yuan X, McCormick K, Yang XH, Chen SJ, Chen RM. The efficacy and safety of rhGH treatment combined with letrozole/GnRHa in adolescent boys. BMC Pediatr. 2025;25(1):59. Additional Declarations No competing interests reported. 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Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-7103844","acceptedTermsAndConditions":true,"allowDirectSubmit":true,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":498890289,"identity":"61dbe70e-5949-408a-a649-fb138af9b38c","order_by":0,"name":"Davoud Amirkashani","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAABBklEQVRIiWNgGAWjYBACeyA+AIQMBkDG4R8VNkCKsfEAPi2GDchaGM6kgbQ04NViAJaFamFmbDvMAOXj0XL8dOLhijN29ubsZw8eLjhz3m5t+2GgLTU20Ti1nMndcPDMjeTEnT15CYdnVNxO3nYmEajlWFpuA06HAbU0fGBOMDiQY3CA58ztZLMDQC2MDYdxazn/FqSl3t7g/BuDA7xt55LNzj8koOUGyJYbhxk33MgxOMzbdsDO7AYBWwxngGw5czxxw403BgdnnElOMLsBtCUBj1/s+XM3f2w4Vg10WI7xhw8VdvZm59MfPvhQY4NTCwZIBKtMIFY52FpSFI+CUTAKRsHIAAAP8nkZaf1COAAAAABJRU5ErkJggg==","orcid":"","institution":"Iran University of Medical Sciences","correspondingAuthor":true,"prefix":"","firstName":"Davoud","middleName":"","lastName":"Amirkashani","suffix":""},{"id":498890290,"identity":"62e0f56c-57b2-4cdc-996b-365254faa140","order_by":1,"name":"Ghazal Tavakoli","email":"","orcid":"","institution":"Iran University of Medical Sciences","correspondingAuthor":false,"prefix":"","firstName":"Ghazal","middleName":"","lastName":"Tavakoli","suffix":""},{"id":498890293,"identity":"0e47c086-fb66-4bd1-a9c4-9e328e2294f7","order_by":2,"name":"Amir Ghanbari","email":"","orcid":"","institution":"Shahid Beheshti University of Medical Sciences","correspondingAuthor":false,"prefix":"","firstName":"Amir","middleName":"","lastName":"Ghanbari","suffix":""},{"id":498890294,"identity":"5e15755f-0cf8-4a72-b0ab-d272c876a02e","order_by":3,"name":"Kiana Orangi","email":"","orcid":"","institution":"Iran University of Medical Sciences","correspondingAuthor":false,"prefix":"","firstName":"Kiana","middleName":"","lastName":"Orangi","suffix":""},{"id":498890296,"identity":"dbd8d641-3924-44a5-a5c6-582632ee19a2","order_by":4,"name":"Fateme Izadi","email":"","orcid":"","institution":"Iran University of Medical Sciences","correspondingAuthor":false,"prefix":"","firstName":"Fateme","middleName":"","lastName":"Izadi","suffix":""}],"badges":[],"createdAt":"2025-07-11 18:08:10","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-7103844/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-7103844/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":89233184,"identity":"ee1ff7a3-9ee5-4b69-92f8-526634394656","added_by":"auto","created_at":"2025-08-17 14:31:51","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":27482,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eMean Heights by Bone Age. \u003c/strong\u003eThis bar chart shows initial height, predicted adult height at the initiation of treatment and the final adult height by the bone age for the group receiving Letrozole and growth hormone.\u003c/p\u003e","description":"","filename":"1.png","url":"https://assets-eu.researchsquare.com/files/rs-7103844/v1/e6ede6d92a3e1c8ad1d18f07.png"},{"id":89232173,"identity":"10f0009c-9aa3-4d2e-96fb-bf5517506acf","added_by":"auto","created_at":"2025-08-17 14:23:51","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":178517,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eRelationship between height augmentation and (A) letrozole treatment duration and (B) baseline bone age, analyzed by piecewise linear regression. \u003c/strong\u003e\u003cem\u003eA. Height gain (cm) increases sharply with increasing letrozole receiving time up to a breakpoint at ~21 months, after which the incremental benefit plateaued. B. Height gain (cm) remained high for boys with bone ages up to 174.1 months (~14.5 years), but declined significantly beyond this threshold, indicating reduced efficacy of letrozole at more advanced skeletal maturity.\u003c/em\u003e\u003c/p\u003e","description":"","filename":"2.png","url":"https://assets-eu.researchsquare.com/files/rs-7103844/v1/38282c0f85e5470871c3638f.png"},{"id":89232179,"identity":"2ca00d83-febe-4e9d-b2f6-20b922722c9a","added_by":"auto","created_at":"2025-08-17 14:23:51","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":17373,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eHeight augmentation (cm) by bone age group (≤14.5 years vs \u0026gt; 14.5 years). \u003c/strong\u003eBoxplots display the median, interquartile range, and whiskers; the group means (5.15 cm vs 2.58 cm for ≤14.5 years and \u0026gt; 14.5, respectively) are annotated.\u003c/p\u003e","description":"","filename":"3.png","url":"https://assets-eu.researchsquare.com/files/rs-7103844/v1/b3640e35a3e9d1f9960cf98b.png"},{"id":90041227,"identity":"6b6d3f24-77e0-46e0-a662-8e86161bba91","added_by":"auto","created_at":"2025-08-27 17:01:33","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":905873,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-7103844/v1/8d17f65a-6335-4c9f-9c17-cb20574e1bd8.pdf"},{"id":89232171,"identity":"c03bbb74-7cd4-425f-844d-684d2b60525f","added_by":"auto","created_at":"2025-08-17 14:23:51","extension":"jpeg","order_by":0,"title":"","display":"","copyAsset":false,"role":"supplement","size":253500,"visible":true,"origin":"","legend":"","description":"","filename":"GraphicalAbstract.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-7103844/v1/15d6e2f3d173e0659c42f9b6.jpeg"}],"financialInterests":"No competing interests reported.","formattedTitle":"\u003cp\u003eAromatase Inhibitor Effectiveness on Height Augmentation: Optimizing Letrozole Therapy for Height Gain in Short-Statured Boys\u003c/p\u003e","fulltext":[{"header":"INTRODUCTION","content":"\u003cp\u003eShort stature is a common reason for referral to pediatric endocrinology clinics and it can cause significant psychological and social stress for both parents and children(1). The most common etiological factors of short stature are Constitutional Growth Delay (CGD), Idiopathic Short Stature (ISS), malnutrition and Growth Hormone Deficiency (GHD) and is a condition in which the height of the individual is more than 2 SD below the corresponding mean height for a given age, sex and population(2, 3). Recombinant human growth hormone (rhGH) is a widely used treatment for short stature; however, it is an expensive medication and typically offers only modest improvements in final height for children who are not growth hormone deficient(1, 4, 5). Notably, approximately 60–80% of children with short stature are classified as having idiopathic short stature (ISS), meaning that no underlying pathology or alternative diagnosis can be identified (1, 6).\u003c/p\u003e\u003cp\u003eAromatase inhibitors (AIs) such as letrozole and anastrozole; have been proposed as an alternative treatment of short stature individually or in combination with rhGH to augment height in male with or without classic GHD (7–9). AIs suppress the conversion of testosterone to estrone and estradiol (E2), the hormone that regulates bone maturation and epiphyseal plate closure which lead to cessions of growth during puberty. In theory, a reduction in estrogen production during the pubertal growth period would permit a longer interval for growth and result in an increase in final adult height. Anastrozole and letrozole are third-generation nonsteroidal AIs that bind to the active site of the aromatase enzyme and block estrogen formation and lead to a significant increase in predicted adult height (PAH) as well as an increased height standard deviation score (HtSDS) for bone age(1, 8, 10).\u003c/p\u003e\u003cp\u003eHowever, the available data on the efficacy of aromatase inhibitor (AI) therapy are limited and sometimes controversial(11, 12). It remains unclear at what specific bone age or under which clinical conditions AI therapy is most effective. This lack of clarity complicates the decision-making process for healthcare providers and emphasizes the need for further research to determine the optimal timing and indicators for implementing AI therapy.\u003c/p\u003e\u003cp\u003eThis article aims to explore the effects of letrozole on final adult height, ascertaining the relationship between its use and changes in growth patterns. Additionally, we will investigate the correlation between timing of letrozole administration concerning patients' bone age with the predicted and actual adult height. By examining the letrozole's administration impact on bone age and height outcomes, we aim to enhance our understanding of its utility in clinical practice and treatment strategies for optimizing adult height among affected individuals.\u003c/p\u003e\u003cdiv id=\"Sec2\" class=\"Section2\"\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003c/div\u003e"},{"header":"METHODS","content":"\u003cp\u003e\u003cb\u003eStudy Design and Participants\u003c/b\u003e\u003c/p\u003e\u003cp\u003eThis study was designed as a retrospective cohort analysis of mid-and late-pubertal male pediatric patients with short stature who were referred to our endocrinology clinic at Ali Asghar Children's Hospital. We reviewed medical records for male patients which a pediatric endocrinologist had confirmed the therapeutic benefit of letrozole (Lz) and started treatment with Lz, meeting inclusion criteria, including chronological age over 11 years, bone age above or equal to 12 years but below or equal to 16 years, diagnosis of growth hormone deficiency (GHD) or idiopathic short stature (ISS) which is defined as height more than 2 standard deviations below the mean height of their similar age and sex group(3). We also include patients which their baseline and follow-up data were available with no missing data, and patients that had no prior treatment with growth hormones, letrozole, or other aromatase inhibitors. We excluded patients with endocrine or genetic disorders, other comorbidities, previous medical treatment for short stature or missing data. Letrozole therapy was initiated based on individual assessment of growth potential and bone age by a pediatric endocrinologist.\u003c/p\u003e\u003cp\u003eThe study population comprised of 40 boys with chronological age over 11 years old with ISS or GHD who were treated with Lz (2.5 mg/day) for a mean duration of 21 months, either as monotherapy or in combination with growth hormone. Nine boys received Lz as monotherapy, while 31 received combined Lz with growth hormone (GH). Lz initiation was individualized based on bone age, growth changes, clinical features, and clinical benefit assessment during follow-ups by the pediatric endocrinologist. Recombinant human growth hormone was given 0.035 mg/kg daily, using the brand CinnaTropin.\u003c/p\u003e\u003cp\u003e\u003cb\u003eMeasurement \u0026amp; Data Collection\u003c/b\u003e\u003c/p\u003e\u003cp\u003eRelevant clinical and laboratory data were extracted from patient records from the endocrinology clinic at Ali Asghar Children's Hospital, including chronological age (CA), bone age assessment using graphic image of the left hand and wrist according to the Greulich and Pyle method, Tanner stage evaluated by comprehensive physical examination performed by an endocrinologist, mid-parental height (MPH), baseline height were measured by standard weight scale, predicted adult height (PAH), which was calculated using established methods (Bayley-Pinneau technique) by an endocrinologist, final adult height (FAH) and duration of letrozole treatment(13, 14). Every 3 months in the pediatric endocrine clinic of Ali Asghar Children's Hospital, examination was performed by the same physician (D.A.) throughout the study. Patients were followed up to reaching FAH characterized as bone age equal or greater than 17 years.\u003c/p\u003e\u003ch2\u003eStatistical Analysis\u003c/h2\u003e\u003cp\u003eData analysis was performed using Python (version 3.12). Continuous variables were reported as mean ± standard deviation and categorical variables were reported as percentages. Comparisons between baseline and follow-up measurements were made using paired t-tests or non-parametric alternatives, such as Wilcoxon signed-rank tests. Spearman correlation coefficients were calculated to assess the relationship between baseline chronological age, bone age and duration of Lz treatment with the final adult height (FAH) and Height augmentation percentage. Height augmentation percentage was calculated with the following formula:\u003c/p\u003e\u003cp\u003eHeight augmentation (%) = (FAH – PAH) / PAH\u003c/p\u003e\u003cp\u003eAdditionally, scatter plots, bar plots and box plots were performed to visualize data distributions and investigate the factors influencing height outcomes. A p-value of less than 0.05 was considered statistically significant.\u003c/p\u003e\u003cp\u003e\u003cb\u003eEthical Considerations\u003c/b\u003e\u003c/p\u003e\u003cp\u003e This study was conducted in accordance with the ethical principles outlined in the Declaration of Helsinki. Ethical approval was obtained from the Ethics Committee of Iran University of Medical Sciences (IR.IUMS.FMD.REC.1404.194).\u003c/p\u003e"},{"header":"RESULTS","content":"\u003cp\u003eThe study population comprised of 40 mid- and late-pubertal boys with a chronological age ranging from 11.5 to 15.5 years. 31 received both Lz and GH, while 9 received Lz as monotherapy (Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e). The mean age of the total population were 13.6 ± 1.15 years at the initiation of treatment. The mean height at baseline was 150.4 ± 5.6 cm, and the mean bone age was 14.2 ± 0.7 years. All patients were treated with letrozole ranging from 1 to 2.5 years for an average duration of 1.8 ± 0.4 years. Sexual maturation was assessed using Tanner staging and from the 40 participants, 21 (52.5%) were classified as Tanner stage IV, 18 (45%) as stage III, and 1 (2.5%) as stage II, with the median of stage III.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cdiv class=\"gridtable\"\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e\u003ctable float=\"Yes\" id=\"Tab1\" border=\"1\"\u003e\u003ccaption language=\"En\"\u003e\u003cdiv class=\"CaptionNumber\"\u003eTable 1\u003c/div\u003e\u003cdiv class=\"CaptionContent\"\u003e\u003cp\u003e\u003cb\u003eAnthropometrics characteristics of the 40 adolescent males receiving Letrozole (Lz) + Growth hormone (GH) or Lz as monotherapy\u003c/b\u003e. \u003cem\u003eValues are expressed as mean ± SD. MPH: Mid parenteral height, SMR: Sexual maturation rate.\u003c/em\u003e\u003c/p\u003e\u003c/div\u003e\u003c/caption\u003e\u003ccolgroup cols=\"3\"\u003e\u003c/colgroup\u003e\u003cthead\u003e\u003ctr\u003e\u003cth align=\"left\" colname=\"c1\"\u003e\u003cp\u003eCharacteristics\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c2\"\u003e\u003cp\u003eLz + GH\u003c/p\u003e\u003cp\u003e(n = 31)\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c3\"\u003e\u003cp\u003eLz\u003c/p\u003e\u003cp\u003e(n = 9)\u003c/p\u003e\u003c/th\u003e\u003c/tr\u003e\u003c/thead\u003e\u003ctbody\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eChronological Age\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e13.52 ± 1.07\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e13.86 ± 1.43\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eBone Age\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e14.13 ± 0.71\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e14.44 ± 0.81\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eInitial Height\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e149.91 ± 5.36\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e151.92 ± 6.55\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eMPH\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e169.26 ± 3.71\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e166.78 ± 3.38\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003ePAH\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e161.67 ± 1.34\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e163.26 ± 0.85\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eSMR\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e3 (median)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e3 (median)\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eMonths with Lz\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e21.68 ± 4.94\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e19.33 ± 5.43\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eMonths with GH\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e15.48 ± 2.46\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e-\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003c/tbody\u003e\u003c/table\u003e\u003c/div\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003ePaired t-tests revealed that both Lz monotherapy and Lz combined with GH produced a highly significant increase in final adult height relative to predicted adult height (p \u0026lt; 0.001), validating letrozole effect on the height augmentation with or without GH (Table\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e). A comparison between Lz and Lz + GH groups also identified greater height increment in the Lz + GH group (4.4cm, 2.3 cm respectively, p = 0.0019) suggesting that Lz + GH might be a better treatment strategy.\u003c/p\u003e\u003cp\u003eSpearman test was also conducted to investigate the correlation between duration of Lz therapy in Lz + GH group and heigh augmentation (cm). A positive correlation was found between the months on Lz therapy and height augmentation (Spearman ρ = 0.703, \u003cem\u003ep\u003c/em\u003e \u0026lt; 0.001). This implies that longer treatment duration is associated with increase in height gains, while piecewise linear regression revealed a breakpoint at 21 months of letrozole treatment. Height augmentation increased up to 21 months, after which the rate of improvement plateaued. This suggests that the main therapeutic benefits are achieved within the first 21 months of therapy (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e-A).\u003c/p\u003e\u003cp\u003eSpearman correlation test was conducted to assess the relationship between height augmentation with the bone age and chronological age which the treatment with Lz + GH started. A significant negative correlation was observed between height augmentation and either bone age (Spearman ρ = -0.367, p-value: 0.0425) or chronological age (Spearman ρ = -0.559, p-value: 0.001). This indicates that as bone age and chronological age increases, the effectiveness of Lz + GH in height enhancement decreases, reinforcing the importance of early intervention.\u003c/p\u003e\u003cp\u003eA segmented regression was conducted to investigate a critical threshold in the relationship between bone age and height augmentation in Lz + GH receiving group. This analysis identified a breakpoint at a bone age of 174 months (~ 14.5 years). Prior to this threshold, height augmentation tended to increase with bone age; however, around 14 years a decline in treatment response was observed suggesting a bone age estimated around 14.5 years threshold for effective letrozole therapy indicating reduced efficacy of letrozole at more advanced skeletal maturity (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e-B). Moreover, a t-test was conducted by categorizing patients into two groups based on the bone age (bone age ≤ 14.5 years and bone age \u0026gt; 14.5 years). Height augmentation was calculated as the difference between final adult height and predicted adult height. Results showed a significantly greater height augmentation in the 14.5 years and younger group (5.15 cm) compared to those older than 14.5 years (2.58 cm). A t-test confirmed that this difference was statistically significant (t = 2.68, p = 0.018), suggesting that earlier initiation of letrozole therapy along with GH (bone age ≤ 14.5 years) is associated with an increase in final adult height (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e).\u003c/p\u003e\u003cp\u003eWe also conducted an independent t-test following categorizing patients into two groups of Tanner stage IV and another group of Tanner stage III and II. The results suggested no significant difference in height augmentation between the two groups (t:1.50, p: 0.14).\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cdiv class=\"gridtable\"\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\"±\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e\u003ctable float=\"Yes\" id=\"Tab2\" border=\"1\"\u003e\u003ccaption language=\"En\"\u003e\u003cdiv class=\"CaptionNumber\"\u003eTable 2\u003c/div\u003e\u003cdiv class=\"CaptionContent\"\u003e\u003cp\u003e\u003cb\u003eComparison of predicted adult height (PAH) versus final adult height (FAH)\u003c/b\u003e, \u003cem\u003ethe absolute and percentage height gains, and paired t-test results for boys receiving letrozole plus growth hormone (Lz + GH) or letrozole monotherapy (Lz). Values are reported mean ± SD; ***p \u0026lt; 0.001 indicates highly significant FAH increase over PAH.\u003c/em\u003e\u003c/p\u003e\u003c/div\u003e\u003c/caption\u003e\u003ccolgroup cols=\"6\"\u003e\u003c/colgroup\u003e\u003cthead\u003e\u003ctr\u003e\u003cth align=\"left\" colname=\"c1\"\u003e\u0026nbsp;\u003c/th\u003e\u003cth align=\"left\" colname=\"c2\"\u003e\u003cp\u003ePAH (cm)\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c3\"\u003e\u003cp\u003eFAH (cm)\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c4\"\u003e\u003cp\u003eFAH-PAH (cm)\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c5\"\u003e\u003cp\u003eHeight\u0026nbsp;augmentation\u0026nbsp;(%)\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c6\"\u003e\u003cp\u003ep\u003c/p\u003e\u003c/th\u003e\u003c/tr\u003e\u003c/thead\u003e\u003ctbody\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e\u003cb\u003eLz + GH\u003c/b\u003e\u003c/p\u003e\u003cp\u003e(n = 31)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\"±\" colname=\"c2\"\u003e\u003cp\u003e161.67 ± 1.34\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e166.07 ± 1.90\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e4.40 ± 2.51\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e2.73%\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e\u003cp\u003e\u0026lt; 0.001 (***)\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e\u003cb\u003eLz\u003c/b\u003e\u003c/p\u003e\u003cp\u003e(n = 9)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\"±\" colname=\"c2\"\u003e\u003cp\u003e163.26 ± 0.85\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e165.56 ± 1.43\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e2.30 ± 1.24\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e1.41%\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e\u003cp\u003e\u0026lt; 0.001(***)\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003c/tbody\u003e\u003c/table\u003e\u003c/div\u003e"},{"header":"Discussion","content":"\u003cp\u003eUtilizing the best strategies to enhance final height in short stature boys is a substantial challenge, due to narrow therapeutic time during puberty and the psychosocial impact of short stature. Moreover, evidence regarding final adult height outcomes following aromatase inhibitor therapy remains limited and inconsistent. We conducted a retrospective analysis of 40 mid and late-pubertal boys with ISS or GHD followed to their final adult height, evaluating the effect of Lz on FAH, identifying treatment duration and bone age thresholds associated with optimal clinical response.\u003c/p\u003e\u003cp\u003eThe timing of therapy initiation emerged as a critical factor in our study. Also, side effects such as increased facial hair may cause social challenges in younger boys, supporting the need to better define the optimal age window for letrozole therapy. We found that boys who began letrozole at a bone age above 14.5 years had significantly lower height augmentation compared to those aged 14.5 years or younger (2.58 cm and 5.15 cm, respectively). This highlights the golden time of starting Lz and the limited residual growth potential once the epiphyses are nearing closure. Varimo et al.(15) initiated Lz in pre- to early-puberty, also implied that too early intervention might not cause significant height gain and highlight the possible optimal treatment window. Our findings are aligned with the general principle that late-puberty offers less time for height gain and the benefits of Lz treatment begin to diminish in this state(16). To conclude, even though our study showed some benefits can still be attained after the bone age of 14.5 years, this improvement is modest compared to earlier intervention. Further research is needed to better define the optimal timing for treatment initiation. Therapy duration is equally important, as height gains had positive correlation with letrozole treatment duration, up to the point of 21 months, after which incremental benefits plateaued. Extending beyond two years may confer only marginal benefit but make them prone to side effects, also discontinuing too soon may result in the loss of a part of the PAH gain. Our study is among the few studies to evaluate the relationship between either letrozole duration or initiation timing and final height gain, providing new insight into the optimal treatment window.\u003c/p\u003e\u003cp\u003eInterestingly, we did not observe any significant difference in efficacy between Tanner stage III and Tanner stage IV at treatment start. This finding is reassuring, as it indicates that boys presenting later in puberty can still benefit from AI therapy while bone age and growth plates suggest possible growth potential. This also highlights the importance of bone age relative to the tanner stage for clinical decision making.\u003c/p\u003e\u003cp\u003eOur findings demonstrated that letrozole therapy with or without GH produced clinically meaningful improvements in height outcomes. FAH significantly exceeded the initial PAH in the treated boys, indicating that monotherapy is effective in promoting height gain, consistent with findings from several previous studies (10, 17\u0026ndash;20). Gavan et al.(18) evaluated the 27 AI treated mid-pubertal boys and reported Lz monotherapy effectively increased height by delaying the bone maturation and making the pubertal growth phase longer. They also pointed at the height gain of 3.8\u0026thinsp;\u0026plusmn;\u0026thinsp;3.5 cm in treatment group compared to only 0.3\u0026thinsp;\u0026plusmn;\u0026thinsp;5.0 cm in untreated controls. Similarly, Rohani et al.(10) reported a significant final height gain of 1.9 cm in CDGP boys treated with Lz. Aligned with the previous studies following patients to their FAH, we found letrozole monotherapy resulted in a height gain of 2.30\u0026thinsp;\u0026plusmn;\u0026thinsp;1.24 cm, reflecting a significant increase relative to PAH.\u003c/p\u003e\u003cp\u003eIn a study by Salehpour et al.(17), 31 of CDGP boys with the bone age of 12.18\u0026thinsp;\u0026plusmn;\u0026thinsp;1.1 treated with Lz for two years. Their findings, while similar in trend, reported a significant increase in PAH (6.1\u0026thinsp;\u0026plusmn;\u0026thinsp;1.9 cm, p\u0026thinsp;\u0026lt;\u0026thinsp;0.01); however, unlike our study, they did not report outcomes to FAH. In contrast, our study following patients to their FAH and demonstrated significant increase in FAH relative to PAH. The greater height gain reported by Salehpour et al. may be attributed to differences of study design and methodologies, as they recalculate PAH after the end of treatment duration, while we followed our patients to their FAH. Additionally, it might be due to initial bone age difference of them having younger population (12.18\u0026thinsp;\u0026plusmn;\u0026thinsp;1.1 years) compared to our study (14.44\u0026thinsp;\u0026plusmn;\u0026thinsp;0.81 years).\u003c/p\u003e\u003cp\u003eOur findings are in contrast with several studies, which found no effect of AI monotherapy on height gain in boys with short PAH(8, 15, 16, 21\u0026ndash;23). This controversy might be due to study design differences. Our study comprised of homogeneous group of mid- to late-pubertal male population followed up to achieve FAH, whereas most of the earlier studies had smaller sample sizes and assessed only changes in PAH without long-term follow-up to FAH. Varimo et al.(15) also followed patients to their final height but reported no significant height gain in the Lz treatment group, while their sample size was smaller(n\u0026thinsp;=\u0026thinsp;10) and they consisted of pre- to early-pubertal boys with the mean bone age of 9.2\u0026thinsp;\u0026plusmn;\u0026thinsp;2.6, while our study focused mainly on mid- to late-pubertal boys with the mean bone age of 14.44\u0026thinsp;\u0026plusmn;\u0026thinsp;0.81 years. This discrepancy suggests that Lz may be less effective in younger bone ages but a more applicable treatment in more advanced bone ages, although future studies are needed to clarify the age range in which letrozole is the most effective.\u003c/p\u003e\u003cp\u003eWe found that the combination of rhGH and Lz led to a significant increase in FAH, with a gain of 4.40\u0026thinsp;\u0026plusmn;\u0026thinsp;2.51 cm above the PAH, highlighting rhGH\u0026thinsp;+\u0026thinsp;Lz as a promising therapeutic strategy for enhancing height outcomes. We also observed greater height increment in the rhGH\u0026thinsp;+\u0026thinsp;Lz group (4.40\u0026thinsp;\u0026plusmn;\u0026thinsp;2.51cm) in comparison with the Lz alone (2.30\u0026thinsp;\u0026plusmn;\u0026thinsp;1.24). Similarly, Maures et al.(19) and several other studies suggested AIs particularly showed better results in combination with GH compared to Lz alone(15, 21, 22). A 2024 meta-analysis confirmed that adding AIs to rhGH leads to higher growth velocity and PAH compared to rhGH as monotherapy, (24). Consistent with the meta-analysis, Zhang et al.(25) concluded rhGH\u0026thinsp;+\u0026thinsp;Lz combination showed better height outcome than the rhGh\u0026thinsp;+\u0026thinsp;GnRH group. These findings collectively underscore rhGH\u0026thinsp;+\u0026thinsp;Lz as a proven superior treatment strategy for maximizing height outcomes in short-statured children.\u003c/p\u003e\u003cp\u003eThis study has several limitations. The modest sample size and retrospective design may cause a selection bias. Choosing the treatment strategy was not randomized, and although we compared final height to each patient's own PAH, confounding factors may remain. Additionally, this study did not assess the safety or side effects, thus further larger prospective trials are needed to evaluate these outcomes. However, this study has important strengths. It is among the few to follow patients to their final adult height, allowing for a more definitive and precise evaluation of treatment efficacy. Moreover, it is the first study to investigate the influence of initial bone ages on letrozole responsiveness, suggesting that the treatment may be more effective at certain bone ages.\u003c/p\u003e"},{"header":"Conclusion","content":"\u003cp\u003eIn summary, we observed that letrozole, both alone and in combination with growth hormone, yields a modest but significant increase in final adult height over the predicted adult height at baseline, with combination therapy producing the better outcomes. Height augmentation positively correlates with letrozole duration up to about 21 months and declines after the bone age of 14.5 years, underscoring the importance of earlier intervention and avoiding overtreatment. Given the lack of comparable research, larger prospective trials are needed to refine optimal age and duration thresholds and to avoid overtreatment and side effects.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eAcknowledgments\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eFunding and Assistance\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe authors received no specific funding for this research.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eConflict of Interest\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe authors declare no conflicts of interest related to this work.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAuthor Contributions\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e\u0026nbsp;All authors contributed to the study design and methods. D.A. collected the data, while G.T. and A.G. wrote the first draft of the manuscript. G.T. performed the statistical analysis and generated the figures for the result section. K.O. reviewed the initial manuscript and designed the graphical abstract. D.A. critically reviewed and edited the manuscript and provided final approval of the manuscript. All authors commented on and revised the manuscript.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003ePrior Presentation\u003c/strong\u003e\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eThis study has not been previously presented at an annual meeting or other conference.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eEthical Approval\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThis study was conducted in accordance with the ethical principles outlined in the Declaration of Helsinki. Ethical approval was obtained from the Ethics Committee of Iran University of Medical Sciences (IR.IUMS.FMD.REC.1404.194).\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eConsent to Publish\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eAll authors have read and approved the final manuscript and give their consent for publication.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eData Availability Statement\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eData will be available due to reasonable requests from the corresponding author.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n\u003cli\u003eZegarra W, Ranadive S, Toulan D, Neely EK. Anastrozole vs Letrozole to Augment Height in Pubertal Males With Idiopathic Short Stature: A 3-Year Randomized Trial. J Endocr Soc. 2024;8(10):bvae141.\u003c/li\u003e\n\u003cli\u003eSultan M, Afzal M, Qureshi SM, Aziz S, Lutfullah M, Khan SA, et al. Etiology of short stature in children. J Coll Physicians Surg Pak. 2008;18(8):493\u0026ndash;7.\u003c/li\u003e\n\u003cli\u003eWit JM, Clayton PE, Rogol AD, Savage MO, Saenger PH, Cohen P. Idiopathic short stature: definition, epidemiology, and diagnostic evaluation. Growth Horm IGF Res. 2008;18(2):89\u0026ndash;110.\u003c/li\u003e\n\u003cli\u003eMauras N, Attie KM, Reiter EO, Saenger P, Baptista J. High dose recombinant human growth hormone (GH) treatment of GH-deficient patients in puberty increases near-final height: a randomized, multicenter trial. Genentech, Inc., Cooperative Study Group. J Clin Endocrinol Metab. 2000;85(10):3653\u0026ndash;60.\u003c/li\u003e\n\u003cli\u003eReiter EO. A brief review of the addition of gonadotropin-releasing hormone agonists (GnRH-Ag) to growth hormone (GH) treatment of children with idiopathic growth hormone deficiency: Previously published studies from America. Mol Cell Endocrinol. 2006;254-255:221\u0026ndash;5.\u003c/li\u003e\n\u003cli\u003eCohen P, Rogol AD, Deal CL, Saenger P, Reiter EO, Ross JL, et al. Consensus statement on the diagnosis and treatment of children with idiopathic short stature: a summary of the Growth Hormone Research Society, the Lawson Wilkins Pediatric Endocrine Society, and the European Society for Paediatric Endocrinology Workshop. J Clin Endocrinol Metab. 2008;93(11):4210\u0026ndash;7.\u003c/li\u003e\n\u003cli\u003eDunkel L. Update on the role of aromatase inhibitors in growth disorders. Horm Res. 2009;71 Suppl 1:57\u0026ndash;63.\u003c/li\u003e\n\u003cli\u003eShams K, Cameo T, Fennoy I, Hassoun AA, Lerner SE, Aranoff GS, et al. Outcome analysis of aromatase inhibitor therapy to increase adult height in males with predicted short adult stature and/or rapid pubertal progress: a retrospective chart review. J Pediatr Endocrinol Metab. 2014;27(7-8):725\u0026ndash;30.\u003c/li\u003e\n\u003cli\u003eVarimo T, Huopio H, Kariola L, Tenhola S, Voutilainen R, Toppari J, et al. Letrozole versus testosterone for promotion of endogenous puberty in boys with constitutional delay of growth and puberty: a randomised controlled phase 3 trial. Lancet Child Adolesc Health. 2019;3(2):109\u0026ndash;20.\u003c/li\u003e\n\u003cli\u003eRohani F, Asadi R, Mirboluk AA, Soheilipour F. Letrozole Effect on Final Height of Patients with Constitutional Delay of Growth and Puberty. Med Arch. 2019;73(5):307\u0026ndash;10.\u003c/li\u003e\n\u003cli\u003eVarimo T, Toiviainen-Salo S, Raivio T, Kerttula L, Dunkel L, Hero M. Letrozole Monotherapy in Pre- and Early-Pubertal Boys Does Not Increase Adult Height. Front Endocrinol (Lausanne). 2019;10:201.\u003c/li\u003e\n\u003cli\u003eGeffner ME. Aromatase inhibitors to augment height: continued caution and study required. J Clin Res Pediatr Endocrinol. 2009;1(6):256\u0026ndash;61.\u003c/li\u003e\n\u003cli\u003eBayley N, Pinneau SR. Tables for predicting adult height from skeletal age: revised for use with the Greulich-Pyle hand standards. J Pediatr. 1952;40(4):423\u0026ndash;41.\u003c/li\u003e\n\u003cli\u003eGreulich WW, Pyle SI. Radiographic atlas of skeletal development of the hand and wrist. The American Journal of the Medical Sciences. 1959;238(3):393.\u003c/li\u003e\n\u003cli\u003eVarimo T, Toiviainen-Salo S, Raivio T, Kerttula L, Dunkel L, Hero M. Letrozole monotherapy in pre-and early-pubertal boys does not increase adult height. Frontiers in Endocrinology. 2019;10:201.\u003c/li\u003e\n\u003cli\u003eFerris JA, Geffner ME. Are aromatase inhibitors in boys with predicted short stature and/or rapidly advancing bone age effective and safe? J Pediatr Endocrinol Metab. 2017;30(3):311\u0026ndash;7.\u003c/li\u003e\n\u003cli\u003eSalehpour S, Alipour P, Razzaghy-Azar M, Ardeshirpour L, Shamshiri A, Monfared MF, et al. A double-blind, placebo-controlled comparison of letrozole to oxandrolone effects upon growth and puberty of children with constitutional delay of puberty and idiopathic short stature. Horm Res Paediatr. 2010;74(6):428\u0026ndash;35.\u003c/li\u003e\n\u003cli\u003eYackobovitch-Gavan M, Tenenbaum A, Phillip M, Lazar L, Oron T. Aromatase-inhibitors Treatment Alone or with GH Increases Final Height in Short-Statured Pubertal Boys - Real-World Data. J Clin Endocrinol Metab. 2025.\u003c/li\u003e\n\u003cli\u003eMauras N, Ross JL, Gagliardi P, Yu YM, Hossain J, Permuy J, et al. Randomized Trial of Aromatase Inhibitors, Growth Hormone, or Combination in Pubertal Boys with Idiopathic, Short Stature. J Clin Endocrinol Metab. 2016;101(12):4984\u0026ndash;93.\u003c/li\u003e\n\u003cli\u003eDutta D, Singla R, Surana V, Sharma M. Efficacy and Safety of Letrozole in the Management of Constitutional Delay in Growth and Puberty: A Systematic Review and Meta-analysis. J Clin Res Pediatr Endocrinol. 2022;14(2):131\u0026ndash;44.\u003c/li\u003e\n\u003cli\u003eLikki SR, Allen HF, Knee A, Tonyushkina KN. Use of letrozole to augment height outcome in pubertal boys: a retrospective chart review. J Pediatr Endocrinol Metab. 2022;35(10):1232\u0026ndash;9.\u003c/li\u003e\n\u003cli\u003ePedrosa LF, de Oliveira JM, Thom\u0026eacute; PRV, Kochi C, Damiani D, Longui CA. Height Increment and Laboratory Profile of Boys Treated With Aromatase Inhibitors With or Without Growth Hormone. Horm Metab Res. 2017;49(10):778\u0026ndash;85.\u003c/li\u003e\n\u003cli\u003eMcGrath N, O'Grady MJ. Aromatase inhibitors for short stature in male children and adolescents. Cochrane Database Syst Rev. 2015;2015(10):Cd010888.\u003c/li\u003e\n\u003cli\u003eWang K, Ye F, Wang DY, Lai PJ, Zhang LQ. Aromatase inhibitors for short stature in male children and adolescents treated with growth hormone: a meta-analysis of randomized controlled trials. BMC Pediatr. 2024;24(1):813.\u003c/li\u003e\n\u003cli\u003eZhang Y, Yuan X, McCormick K, Yang XH, Chen SJ, Chen RM. The efficacy and safety of rhGH treatment combined with letrozole/GnRHa in adolescent boys. BMC Pediatr. 2025;25(1):59.\u003c/li\u003e\n\u003c/ol\u003e\n\u003cp\u003e\u0026nbsp;\u003c/p\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":true,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true},"keywords":"Letrozole, Aromatase Inhibitors, Growth hormone, Short-stature","lastPublishedDoi":"10.21203/rs.3.rs-7103844/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-7103844/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003ch2\u003eBackground\u003c/h2\u003e\u003cp\u003eAromatase inhibitors (AIs) such as letrozole (Lz) have proposed to increase final adult height by delaying epiphyseal closure through reducing estrogen synthesis, but optimal timing for initiation and duration of treatment remains unclear.\u003c/p\u003e\u003ch2\u003eObjective\u003c/h2\u003e\u003cp\u003eTo evaluate the effect of Lz, with or without recombinant human growth hormone (rhGH), on final adult height (FAH) and to identify treatment duration and bone age thresholds that maximize clinical responsiveness.\u003c/p\u003e\u003ch2\u003eMethods\u003c/h2\u003e\u003cp\u003eA retrospective cohort study of 40 boys with bone age of 12\u0026ndash;16 years with the diagnosis of idiopathic short stature (ISS) or growth hormone deficiency (GHD) and no prior history of growth-modulating therapy followed to their FAH. They have been treated with Lz (2.5 mg/day) for 1 to 2.5 years. Nine received Lz as monotherapy and 31 received Lz\u0026thinsp;+\u0026thinsp;rhGH.\u003c/p\u003e\u003ch2\u003eResults\u003c/h2\u003e\u003cp\u003eBoth letrozole monotherapy and combination therapy demonstrated significant increases in FAH versus predicted adult height (PAH) with the height augmentation of 2.30\u0026thinsp;\u0026plusmn;\u0026thinsp;1.24 cm and 4.40\u0026thinsp;\u0026plusmn;\u0026thinsp;2.51 cm, respectively (p\u0026thinsp;\u0026lt;\u0026thinsp;0.001). In the Lz\u0026thinsp;+\u0026thinsp;rhGH group, height augmentation positively correlated with treatment duration up to a 21-month breakpoint (ρ\u0026thinsp;=\u0026thinsp;0.703, p\u0026thinsp;\u0026lt;\u0026thinsp;0.001), while beyond that point, the effectiveness decreased significantly. Notably, height augmentation negatively correlated with baseline bone age (ρ = \u0026minus;\u0026thinsp;0.367, p\u0026thinsp;=\u0026thinsp;0.0425). Patients treated at or below a bone age of 14.5 years gained 5.15 cm compared to 2.58 cm in older boys (p\u0026thinsp;=\u0026thinsp;0.018).\u003c/p\u003e\u003ch2\u003eConclusions\u003c/h2\u003e\u003cp\u003eAdministering Lz with GH after a bone age of 14.5 years showed a significant decrease in height augmentation. Moreover, extending Lz therapy up to 21 months enhances this gain, while benefits appear to decrease significantly beyond that point. Early initiation and careful optimization of treatment duration maximize efficacy and minimize the risk of overtreatment and adverse effects.\u003c/p\u003e","manuscriptTitle":"Aromatase Inhibitor Effectiveness on Height Augmentation: Optimizing Letrozole Therapy for Height Gain in Short-Statured Boys","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-08-17 14:23:46","doi":"10.21203/rs.3.rs-7103844/v1","editorialEvents":[{"type":"communityComments","content":0}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"c3980403-97af-4e78-bee2-42dd8aea2841","owner":[],"postedDate":"August 17th, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[],"tags":[],"updatedAt":"2025-08-27T16:53:26+00:00","versionOfRecord":[],"versionCreatedAt":"2025-08-17 14:23:46","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-7103844","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-7103844","identity":"rs-7103844","version":["v1"]},"buildId":"XKTyCvWXoU3ODBz1xrDgd","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}