Changes in CA125 and CA19-9 Biomarkers and Lesion Size in Deep Infiltrating Endometriosis Patients Treated with Dienogest

& Objective: Deep Infiltrating Endometriosis (DIE) is a severe form of endometriosis with limited tools for objective assessment of therapeutic efficacy. Although CA125 and CA19‑9 are elevated in many patients, their utility in monitoring response to hormonal therapyethi remains unclear. This study was conducted with aim to evaluate the changes in imaging findings and the biomarkers CA125 and CA19-9 in Deep Infiltrating Endometriosis (DIE) patients who underwent Dienogest (DNG) treatment.

& Methods: This prospective cohort study was conducted on women diagnosed with DIE over a 6 -month period at Kamali Hospital in Alborz, Iran. All participants received consistent oral Verogest 2 mg daily for six months. Endometriosis infiltration depth as well as CA12 5 and CA19 -9 serum levels were assessed at the baseline and six months after DNG treatment. Data were analyzed using SPSS software (version 22.0). P<0.05 was considered as statistically significant.

The study included 87 DIE patients, with a mean age 37.6±6.4 years and a median duration of endometriosis of 4.0 years (Interquartile Range (IQR): 2.0-8.0). The median size of endometriosis lesions significantly decreased from 7.0 cm (IQR: 4.0- 14.0 cm) at baseline to 4.0 cm (IQR: 2.0-9.5 cm) after six months of DNG treatment (P<0.001); the median decrease in lesion size was -34.6% (-55.8%, -16.7%). CA125 levels significantly decreased from a median of 80.0 (IQR: 46.3-101.0) to 40.0 (30.0- 73.0), and CA19-9 levels decreased from 68.0 (45.0-96.2) to 34.0 (28.0-56.0) (P<0.001 for both). The treatment was well tolerated, with no clinically significant adverse effects reported among the patients.

These findings suggest that DNG may be an effective therapeutic option for the management of DIE, leading to improvements in both imaging characteristics and relevant biomarkers.

Deep infiltrating endometriosis, Dienogest, CA125, CA19 -9, Endometriosis lesion size Received: 2025/02/12 Accepted: 2025/04/26 Published Online: 18 Jul. 2026 Corresponding Information: Mahin Seifi Alan, Cardiovascular Research Center, Alborz University of Medical Sciences, Karaj, Iran Email: [email protected] Copyright © 2026, This is an original open-access article distributed under the terms of the Creative Commons Attribution-noncommercial 4.0 International License which permits copy and redistribution of the material just in noncommercial usages with proper citation . 1. Introduction Deep Infiltrating Endometriosis (DIE) is a severe form of endometriosis marked by the invasion of endometrial-like tissue into adjacent structures outside the uterus, such as the uterosacral ligaments, bladder, and rectum (1). The persistent challenges in managing of DIE have prompted a growing interest in exploring new therapeutic options to enhance its clinical outcomes in recent years (2). Given the pivotal role of estrogen in the development and progression of endometriosis, hormonal treatments such as Combined Hormonal Contraceptives (CHC) and progestin are currently utilized as first -line therapeutic options in affected individuals (3-5). Dienogest (DNG), a unique fourth -generation progestin, which selectively binds to progesterone receptors, has emerged as a promising pharmacological agent in managing this condition. In vivo and vitro studies, DNG shows strong progestogenic effectiveness alongside moderate estrogen-suppressing effects. Additionally, it exhibits anti -inflammatory, 831 CA125, CA19-9, and Lesion Size in Endometriosis Volume 11, September 2026 Journal of Obstetrics, Gynecology and Cancer Research anti-proliferative, and antiangiogenic properties that effectively decrease the growth of endometrial -like tissue (6,7). CA125 and CA19 -9 biomarkers, produced by cells in the ovaries, fallopian tubes, and gastrointestinal tract, exhibit elevated levels in women with endometriosis attributed to the inflammation and irritation in these regions. Given their association with the severity of endometriosis, a decrease in their levels could potentially indicate treatment success (8-11). Available evidence on the value of DNG in treating DIE is still limited and mainly focused on subjective parameters such as pain relief and quality of life to assess the effectiveness of endometriosis treatments (12-15). Therefore, the present study was conducted with aim to monitor changes in biomarkers CA125 and CA19-9, as well as changes in imaging findings to track disease activity and response to treatment. 2. Materials and Methods This prospective observational cohort study was conducted on women diagnosed with DIE over a 6 - month period at Kamali Hospital in Alborz, Iran. The study included women with confirmed DIE in the uterosacral ligaments through imaging or surgical findings. T he pregnant women, and individual with pelvic infections, abscesses, or cancer were not included. None of the women in this study had undergone prior surgical treatment for endometriosis. Participants received DNG treatment in the form of oral Verogest 2 mg tablets, taken once daily throughout the study duration. Serum levels of the biomarkers CA125 and CA19 -9 were evaluated using ELISA at baseline and 6-month follow-up. Endometriosis lesion size was assessed by specialized sonographers using a comprehensive approach involving three -dimensional transvaginal/transrectal and abdominal ultrasound at baseline and 6 months after treatment. Demographic and clinical characteristics, including age, Body Mass Index (BMI), endometriosis grade, and, marital status, employment status, education, Sexual Transmitted Disease (STD), smoking, hormonal contraceptive, previous Cesarean section, age at first delivery, number of delivery, endometriosis duration were collected using a checklist at study visits. The data were summarized using appropriate descriptive statistics, mean ( Standard Deviation [SD]) or median (Interquartile Range [IQR]), for continuous variables and frequency (%) for categorical variables. Paired data on biomarkers levels and lesion size was analyzed using Wilcoxon signed -rank test. All statistical analyses were performed using SPSS version 22.0. P<0.05 was considered as statistically significant. 3. Results The study included 87 patients diagnosed with DIE in the uterosacral ligaments, with an average age of 37.6±6.4 years. All participants completed the study. Among the participants, 74.7% (n=65) were married, 41.9% (n=36) had an Academic education, and 54% (n=47) were employed. Additionally, 20% had a history of STDs, 8% were current smokers, and 6% were using hormonal contraceptives. A total of 39.5% had a history of cesarean section. Furthermore, 7.1% were classified as overweight or obese (BMI>25.0 kg/m2). Regarding endometriosis grading, the majority (69%) were classified as grade IV and none of the participants had grade I. The median duration of endometriosis was 4.0 years (IQR: 2.0 -8.0) (Table 1). Overall, a reduction in the DIE Size was observed in 80.0% (64/80) of participants, but increased 6% (5/80) or remained unchanged 14% (11/80) in others. The median endometriosis lesion size significantly decreased from 7.0 cm (interquartile range: 4.0 -14.0 cm) at baseline to 4.0 cm (interquartile range: 2.0 -9.5 cm) after six months of DNG treatment, representing a median reduction of 34.6% (interquartile r ange: - 55.8% to -16.7%) (P<0.001) (Table 2). To assess the impact of DNG on CA125 and CA19 - 9 biomarker levels, the analysis focused on participants with abnormal levels of these markers. Initially, 61.2% (52/85) of participants exhibited elevated CA125 levels, which decreased to 38.5% (32/83) after s ix months of treatment. The median CA125 level in these individuals significantly decreased from 80.0 (46.3, 101.0) to 40.0 (30.0, 73.0). Similarly, 57.0% (49/86) of participants had abnormal CA19 -9 levels at baseline, which decreased to 26.2% (22/84) post -treatment. The median CA19 -9 level in these participants also significantly decreased from 68.0 (45.0, 96.2) to 34.0 (28.0, 56.0) (P<0.001) (Table 2). None of the participants reported experiencing any severe adverse events associated with DNG treatment, such as persistent nausea and vomiting, jaundice, dark urine, or severe abdominal pain. Shima Mohammadian, et al. 832 Volume 11, September 2026 Journal of Obstetrics, Gynecology and Cancer Research Table 1. Baseline characteristics of participants Baseline Characteristics Percent%(Frequency)/ Mean (SD)/ Median (IQR) Age (year), Mean (SD) 37.6(6.4) Marital status, % (N) Married 74.7%(65) Divorced 11.5%(10) Non married 13.8%(12) Employment status, % (N) Employed 54.0%(47) Non employed 46.0%(40) education, % (N) Elementary School 12.8%(11) High school 45.3%(39) Academic education 41.9%(36) STD (Yes), % (N) 20.0%(17) Smoking (Yes), % (N) 8.0%(7) Hormonal contraceptive (Yes), % (N) 6.0%(5) Previous Cesarean Section (yes), % (N) 39.5%(34) Age at first delivery, Mean (SD) 23.2(4.6) Number of delivery, Median (IQR) 1.0(0.0, 2.0) BMI % (N) Under weight 15.5%(13) Normal 77.4%(65) Over weight/obese 7.1%(6) Endometriosis grade, % (N) I 0.0%(0) II 15.5%(13) III 15.5%(13) IV 69%(58) Endometriosis duration, Median (IQR) 4.0(2.0-8.0) SD: Standard Deviation, BMI: Body Mass Index, IQR: Interquartile Range, N: Number Table 2. Changes in CA125 and CA19-9 Biomarkers and Lesion Size in participants CA125 biomarker CA19-9 biomarker DIE Size in Sonography Median scores (IQR) Baselinea 80.0(46.3, 101.0) 68.0(45.0, 96.2) 7.0(4.0, 14.0) 6 month after treatment 40.0(30.0, 73.0) 34.0(28.0, 56.0) 4.0(2.0, 9.5) % Difference -26.9(-51.1, -4.0) -25.8(-48.3, -7.7) -34.6%(-55.8, -16.7) P-value <0.001 <0.001 <0.001 % abnormalb Baseline 61.2%(52/85) 57.0%(49/86) NA 6 month after treatment 38.5%(32/83) 26.2%(22/84) NA P-value <0.001 35 U/mL and CA19-9>37 U/mL 833 CA125, CA19-9, and Lesion Size in Endometriosis Volume 11, September 2026 Journal of Obstetrics, Gynecology and Cancer Research 4. Discussion The purpose of this study was to assess the impact of DNG treatment on imaging findings and the levels of the biomarkers CA125 and CA19 -9 in patients with DIE. The results showed that after six months of DNG treatment, the majority of patients demonstrated reductions in the levels of CA125 and CA19 -9, with approximately half of the participants having these biomarkers fall within the normal range. Furthermore, the study found a significant decrease of around 40% in the median size of DIE lesions. Regarding safety, in our study, none of the patients experienced severe side effects during the study. In line with our research, Piacenti et al. reported that the mean size of DIE lesions decreased from 16±5.2 mm at baseline to 8.7±2.8 mm at 6 months after treatment with DNG, representing an approximately 45% reduction (16). Other previous studies investigating the use of DNG in treating endometriosis, have also reported that DNG efficiently reduced the size of endometriotic lesions (16-19); overall, they found a reduction in the mean lesion volume ranging from 41% to 75% after 6 months (17-19), and up to 76% after 12 months of DNG treatment (19). In our study, approximately 60% of patients with DIE had elevated levels of CA125 and/or CA19 -9. Findings from a meta -analysis have indicated that serum levels of CA125 and CA19 -9 may serve as useful biomarkers for the noninvasive diagnosis of endometriosis (20). Furthermore, a recent study found that women with DIE had higher serum levels of CA125 compared to those with ovarian endometrioma but without DIE (21). Additionally, some researchers have argued that the serum levels of CA125 and CA19 -9 could act as indicators for assessing the therapeutic response in patients with DIE. Consistent with our findings, a study conducted on 121 women diagnosed with recurrent endometriosis revealed a significant decrease in mean CA125 levels from 80.04 U/mL at baseline to 33.11 U/mL after 6 months of treatment with DNG (22). In the present study, a small proportion of participants did not experience a reduction in DIE lesion size (20%) or serum levels of CA125 (10%) and CA19-9 (2%) in response to DNG treatment. Direct comparisons with previous studies are challenging due to di fferences in patient populations, definitions of efficacy, and primary outcome measures, which have led to a wide range of reported non -response rates, ranging from 0.3% to 13.22% in different studies (22- 27). There could be several reasons why some patients may not respond well to DNG treatment; these reasons include the advanced severity of their endometriosis, individual variations in medication response, the development of drug resistance over time, underl ying health factors or genetic predispositions affecting treatment effectiveness, potential misdiagnosis leading to ineffective therapy, or patient non -compliance with the prescribed treatment plan. Regarding the mechanism of action, DNG is a hybrid progestin with excellent oral bioavailability and a potent progestational impact. It inhibits gonadotropin secretion, exhibits localized antiproliferative and anti - inflammatory effects on endometriotic les ions, and creates a predominantly gestagenic endocrine environment, ultimately resulting in the reduction of endometriotic lesions (28-30). Additionally, DNG has been shown to suppress ovulation and enhance the responsiveness to progestin treatment in endometriotic tissue (29,31,32). In our study, none of the patients experienced any severe side effects during the treatment period. The safety profile of DNG appears generally satisfactory for individuals with endometriosis, as demonstrated in clinical trials where DNG 2 mg exhibited goo d tolerability for up to 65 weeks. In a study on the safety and tolerability of dienogest in endometriosis, common adverse events occurred in less than 10% of patients and were generally mild to moderate in severity (23). Long-term use of DNG for up to 5 years has also shown a favorable safety profile (33,34). Treatment with DNG 2 mg can lead to endometrial regression and irregular bleeding, which may decrease over time. The occurrence of amenorrhea varied during treatment, and although spotting may occur with long-term DNG use, it resulted in very few discontinuations in clinical trials (23,35). Initiating DNG 2 mg at the beginning of menses or using a GnRH agonist before starting long - term DNG therapy may help reduce the initial irregular bleeding. Consistent and regular intake of DNG is essential to maintain the ovulation blockade due to its short half-life (36,37). 5. Conclusion The results of this study indicated that DNG could be a promising therapeutic option for patients with DIE. The reductions in endometriosis lesion size, as well as the significant decreases in the biomarkers CA125 and CA19-9, suggest that DNG treatment may lead to meaningful improvements in both radiographic and biochemical markers of disease. 6. Declarations Acknowledgments The researchers appreciated the Clinical Research Development Units of Kamali Hospital in Alborz University of Medical Sciences. Ethical Considerations The study was approved by ethics committee of Alborz University of Medical Sciences, Alborz, Iran, and all participants provided written informed consent (IR.ABZUMS.REC.1401.317). Shima Mohammadian, et al. 834 Volume 11, September 2026 Journal of Obstetrics, Gynecology and Cancer Research Authors' Contributions Shima Mohammadian: Conceptualization, Data curation, Investigation, Writing - original draft, Visualization. Mahin Seifi Alan: Methodology, Formal analysis, Validation, Writing - original draft, Writing - review and editing, Supervision, Project administration. Zahra Sadat Khonsarian: Investigation, Resources, Data collection, Validation. Kobra Hosseini: Software, Formal analysis, Writing - review and editing. Haniyeh Rashidi: Data collection, Formal analysis, Writing- review and editing. All authors have read and approved the final version of the manuscript and agree to be accountable for all aspects of the work. Conflict of Interest The authors declare that they have no conflict of interest. Fund or Financial Support Not applicable. 1. Tosti C, Pinzauti S, Santulli P, Chapron C, Petraglia F. Pathogenetic mechanisms of deep infiltrating endometriosis. Reprod Sci. 2015;22(9):1053-9. [doi:10.1177/1933719115592713] 2. D’Alterio MN, D’Ancona G, Raslan M, Tinelli R, Daniilidis A, Angioni S. Management Challenges of Deep Infiltrating Endometriosis. Int J Fertil Steril. 2021;15(2):88 -94. [doi:10.22074/ijfs.2020.134689] 3. Kalaitzopoulos DR, Samartzis N, Kolovos GN, Mareti E, Samartzis EP, Eberhard M, et al. 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Eur J Obstet Gynecol Reprod Biol. 2011;157(2):212-6. [doi:10.1016/j.ejogrb.2011.03.012] 37. Murji A, Biberoğlu K, Leng J, Mueller MD, Römer T, Vignali M, et al. Use of dienogest in endometriosis: a narrative literature review and expert commentary. Curr Med Res Opin. 2020;36(5):895-907. [doi:10.1080/03007995.2020.1744120] How to Cite This Article: Mohammadian Sh, Seifi Alan M, Sadat Khonsarian Z, Hosseini K, Rashidi H. Changes in CA125 and CA19 -9 Biomarkers and Lesion Size in Deep Infiltrating Endometriosis Patients Treated with Dienogest . J Obstet Gynecol Cancer Res. 2026;11(9):830-836. Download citation: RIS | EndNote | Mendeley |BibTeX |