Masked by Eosinophils: A Cryptic Presentation of Paediatric B-ALL with IGH::IL3 Rearrangement

Masked by Eosinophils: A Cryptic Presentation of Paediatric B-ALL with IGH::IL3 Rearrangement | 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 Case Report Masked by Eosinophils: A Cryptic Presentation of Paediatric B-ALL with IGH::IL3 Rearrangement Parimal Sarda, Himil Parikh, Sandip Shah This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-6751831/v1 This work is licensed under a CC BY 4.0 License Status: Under Review Version 1 posted 9 You are reading this latest preprint version Abstract Hypereosinophilia is uncommon in the paediatric population and may be associated with either primary or secondary conditions. In a very small proportion of cases (less than 1%), it forms part of the initial presentation of acute lymphoblastic leukemia (ALL). More frequently, hypereosinophilia appears before overt leukemia symptoms develop, which can delay diagnosis and place affected children at increased risk due to the lack of early intervention. We recently reviewed a case of 6½-year-old female who presented with hypereosinophilia and no circulating blasts. Bone marrow showed significant prominence of eosinophils and their precursors with ~ 2% blasts on morphology. Bone marrow biopsy was received for review and showed a significant burden of immature cells/blasts which on immunohistochemistry was revealed as B-acute lymphoblastic leukemia (B-ALL). Cytogenetics by Fluorescence in-situ hybridization (FISH) showed IGH rearrangement while the routine karyotyping as well as Next Generation Sequencing (NGS) were both negative for any genetic aberrancy. This case highlights the importance of a thorough marrow evaluation in paediatric eosinophilia and discusses the challenges in identifying cryptic rearrangements that are not evident on standard cytogenetic and molecular panels. Figures Figure 1 Figure 2 Introduction Hypereosinophilia (HE) is uncommon in children and is typically associated with allergic, parasitic, or autoimmune disorders. Rarely—accounting for less than 1% of cases—it may precede or accompany hematologic malignancies such as acute lymphoblastic leukemia (ALL). One such rare entity is B-ALL with IGH::IL3 rearrangement [formerly known as t(5;14) ], a World Health Organization (WHO)-recognized subtype characterized by interleukin-3 overproduction leading to marked eosinophilia, often without circulating blasts.[ 1 ] Despite HE being a feature of numerous conditions, including neoplasms, the presence of more common causes often diverts attention from underlying hematologic malignancies, delaying diagnosis and treatment. Furthermore, IGH rearrangements can be cryptic and may escape detection on conventional karyotyping. They are also frequently absent from standard next-generation sequencing (NGS) panels used for leukemia or lymphoma workups. Case Presentation A 6½-year-old female (height 109 cm, weight 16.5 kg, BMI 13.89) presented with the complaints of abdominal pain, fever, and burning, itchy rashes over the palms and soles for 5–7 days. On examination, patient did not have any enlarged lymph nodes. The abdomen was soft without any guarding or rigidity and had no palpable hepatosplenomegaly. A routine complete blood count (CBC) showed leukocytosis with WBC count of 204 × 10 9 /L, Hb 11.1 g/dL, and platelet count of 187 x 10 9 /L. Eosinophils constituted 80% of the leukocytes with an absolute eosinophil count of 1.63 lakh/µL. There were no circulating blasts noted on the peripheral smear. LDH was notably elevated (788 U/L). In view of complaint of abdominal pain, an ultrasound of the abdomen was performed which showed mild ascites and congestive hepatomegaly. Spleen was however normal in size. 2D echocardiography was done as a part of work-up for hypereosinophilia which revealed acute eosinophilic myocarditis with LVEF 50–55% and a follow-up troponin (TROP-I) was also elevated with the levels of 5339.2 ng/ml. Magnetic Resonance Imaging (MRI) brain suggested acute/subacute infarcts. An outside marrow aspirate report showed 2% blasts with 55% eosinophils. Megakaryocytes were adequate with normal morphology. However, immunophenotyping by flowcytometry was also done outside which showed ~ 10% suspicious B-lymphoblasts and the overall findings were interpreted as myeloid/lymphoid neoplasm with eosinophilia. Cytogenetics & Next generation sequencing were performed, however all of that turned out to be negative. In view of the above reports, patient was started on Hydroxyurea & Naproxen. We received this case for review at our centre where we confirmed peripheral blood eosinophilia with ~ 91% eosinophils and no circulating blasts. The total count was now 149 x 10 9 /L (probably due to hydroxyurea therapy) with the differential count showing neutrophils- 01%, lymphocytes- 03%, monocytes- 01%, basophils- 03% and eosinophils- 91%. The absolute eosinophil count was 135 x 10 9 /L. We did not receive bone marrow aspirate and hence were not able to review the same at our end. The bone marrow biopsy for review was hypercellular (~ 100%) with interstitial immature precursors along with hyperplasia of the eosinophils and their precursors as shown in Fig. 1 . We went ahead with the immunohistochemistry panel as represented in Fig. 2 , which showed that the blasts were positive for CD10, PAX5, CD79a, TdT, CD34 constituting ~ 35–40% of total cellularity while being negative for CD3, CD5, CD117 and CD20 (not shown). Hence the final diagnosis we gave was in favour of B-Acute lymphoblastic leukemia (B-ALL). B-ALL with hypereosinophilia showing an IGH gene rearrangement is a recurrent cytogenetic abnormality mentioned as separate entity in WHO classification of haematolymphoid neoplasms. We therefore reviewed the cytogenetics & NGS data and found that IGH::IL3 fusion/rearrangement was not included in the FISH & NGS panels and hence was ordered from our side using a break-apart FISH for IGH as IL3 probe was not available in our region. IGH break-apart FISH was performed on heparinized bone marrow aspirate and turned out to be positive in ~ 7% cells. As the burden of blasts was very low in the bone marrow aspirate (~ 10% on immunophenotyping by flowcytometry), this explained the low percent positivity on FISH and was considered to be a cryptic IGH rearrangement likely an IGH::IL3 fusion resulting in this marked eosinophilia causing organ involvement. Discussion This case highlights the diagnostic challenge of B-lymphoblastic leukemia (B-ALL) presenting with hypereosinophilia in the absence of circulating blasts. Cryptic IGH::IL3 rearrangements may evade detection by conventional cytogenetics, and standard next-generation sequencing (NGS) panels often lack coverage for such atypical fusions. Thus, heightened clinical and molecular awareness is essential when interpreting negative or inconclusive molecular results. Notably, a 2021 study demonstrated that mate-pair sequencing offers superior sensitivity in detecting IGH::IL3 fusions compared to traditional diagnostic approaches.[ 2 ] A comprehensive analysis of 24 patients—one of the largest series to date—by Fournier et al. reported a median total leukocyte count of 72 × 10⁹/L and a median eosinophil count of 32 × 10⁹/L, with peripheral blood blasts ranging from 0 to 37 × 10⁹/L. Notably, in 5 of their own 8 cases, no peripheral blasts were detectable.[ 1 ] In our case, both the total leukocyte count and absolute eosinophil count were higher than their cohort, yet, consistent with the majority of their findings, circulating blasts were absent. This observation is diagnostically significant: it underscores the need for a low threshold of suspicion for hematologic neoplasms, especially when peripheral blood findings are non-revealing. The eosinophilia observed in such cases is likely reactive, driven by aberrant cytokine production—particularly IL-3—associated with cryptic IGH::IL3 fusions. This not only explains the marked eosinophilia and potential for organ infiltration but also contributes to a dilutional effect on blast percentages in both peripheral blood and bone marrow, complicating morphological assessment. In our patient, this dilution likely masked the presence of malignant blasts on morphology, particularly challenging in paediatric cases where hematogones can mimic or obscure lymphoblasts. Flow cytometry played a critical role in our diagnosis, revealing approximately 10% blasts with a B-lymphoblast phenotype, which were morphologically indistinct and may have otherwise been misclassified. Fournier et al. similarly described a case initially misdiagnosed due to negative findings on conventional FISH and karyotyping, later confirmed via NGS to harbor an IGH::IL3 fusion.[ 1 ] This reinforces the need for including IGH::IL3 probes in targeted NGS panels, especially in paediatric B-ALL with eosinophilia, as timely identification of such fusions can significantly impact prognosis and therapeutic decisions. While most paediatric B-ALL cases carry a favorable prognosis, IGH::IL3-positive leukemias are considered to have intermediate risk according to WHO guidelines. In our case, we were fortunate to detect the IGH rearrangement by FISH despite the low blast burden in the aspirate—a reminder of the importance of integrating cytogenetic, flow cytometric, and molecular data for accurate diagnosis. A recent study from the United States examining hypereosinophilia in the paediatric age group emphasized the importance of maintaining a low threshold for investigating hematological malignancies in such patients. Although only one case of acute lymphoblastic leukemia (ALL) was identified among their cohort—accounting for < 1% of total cases[ 3 ]—the clinical implications are profound, as early diagnosis can dramatically alter the disease trajectory through timely initiation of appropriate therapy. Several key considerations should be kept in mind when evaluating a paediatric patient with eosinophilia. Hypereosinophilia accompanied by clinical symptoms and biochemical or radiologic signs of organ involvement warrants a high index of suspicion for both clonal eosinophilic syndromes and reactive eosinophilia secondary to an underlying neoplasm. The International Cooperative Group on Eosinophil Disorders (ICOG-EO) has recently revised the definition of persistent eosinophilia by reducing the required duration from 4 weeks to 2 weeks[ 4 ], acknowledging that significant organ damage may already occur by the 4-week mark, and that earlier intervention is critical. In India, where parasitic infections remain endemic, empirical administration of anti-helminthics is a common first-line practice. Consequently, patients may already have received antiparasitic treatment by the time they present to a tertiary centre, even when referred from remote areas. Therefore, in any case where a more ominous underlying process is suspected, bone marrow aspiration and trephine biopsy should not be delayed. While biopsies are sometimes avoided due to perceptions of invasiveness, particularly in paediatric settings, it is essential to recognize their diagnostic value. Flow cytometry relies heavily on aspirate quality and may yield inconclusive results in cases with low blast burden or hypocellular aspirates. In such situations, a trephine biopsy coupled with immunohistochemistry remains indispensable for diagnostic accuracy. Our case further supports the World Health Organization (WHO) classification of B-ALL with t(5;14)(q31;q32)/IGH::IL3 fusion as a distinct clinicopathologic entity. It demands heightened clinical vigilance and the use of advanced diagnostic platforms—including flow cytometry, FISH, and NGS—to ensure timely and accurate diagnosis. Conclusion B-lymphoblastic leukemia (B-ALL) with IGH::IL3 rearrangement represents a rare paediatric subtype that may present with marked hypereosinophilia and little to no circulating blasts. This case highlights the critical importance of comprehensive bone marrow evaluation and the application of advanced molecular diagnostics in atypical presentations. Heightened awareness of this entity is essential to avoid misdiagnosis, ensuring timely initiation of appropriate therapy and potentially improving clinical outcomes. Declarations Author contributions: P.S. contributed to the conceptualisation, manuscript drafting and writing, analysis of histopathological and immunohistochemical data. Additionally, P.S. was involved in the interpretation of cytogenetics and molecular data, as well as the review and editing of the manuscript. H.P. contributed to the conceptualization, drafting, and writing of the manuscript, conducted histopathological and immunohistochemical analysis, prepared figures and imaging, and participated in the review and editing of the manuscript. S.S. provided clinical supervision, contributed to the conceptualization, and participated in the review and editing of the manuscript. Funding disclosure: This study was not supported by any funding. Conflicts of interest: The authors declare that they have no conflict of interest. Ethics approval statement (if applicable): Ethical approval was not required for this case report as this case was derived retrospectively and none of the patient’s identification has been revealed. Written informed consent was obtained from the patient for the publication of this report and any accompanying images. Patient consent statement (if applicable): Written informed consent was obtained from the parents. Consent for publication: Consent for publication was obtained from the parents. References Fournier B, Balducci E, Duployez N et al (2019) B-ALL With t(5;14)(q31;q32); IGH-IL3 Rearrangement and Eosinophilia: A Comprehensive Analysis of a Peculiar IGH-Rearranged B-ALL. Front Oncol 9:1374 Guenzel AJ, Smadbeck JB, Golden CL et al (2021) Clinical utility of next generation sequencing to detect IGH/IL3 rearrangements [t(5;14)(q31.1;q32.1)] in B-lymphoblastic leukemia/lymphoma. Ann Diagn Pathol 53:151761 Ness TE, Erickson TA, Diaz V et al (2023) Pediatric Eosinophilia: A Review and Multiyear Investigation into Etiologies. J Pediatr 253:232–237e1 Valent P, Klion AD, Roufosse F et al (2023) Proposed refined diagnostic criteria and classification of eosinophil disorders and related syndromes. Allergy 78:47–59 Additional Declarations No competing interests reported. Cite Share Download PDF Status: Under Review Version 1 posted Editorial decision: Revision requested 17 Jun, 2025 Reviews received at journal 16 Jun, 2025 Reviews received at journal 05 Jun, 2025 Reviewers agreed at journal 03 Jun, 2025 Reviewers agreed at journal 03 Jun, 2025 Reviewers invited by journal 03 Jun, 2025 Editor assigned by journal 02 Jun, 2025 Submission checks completed at journal 02 Jun, 2025 First submitted to journal 26 May, 2025 You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. We do this by developing innovative software and high quality services for the global research community. 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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-6751831","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Case Report","associatedPublications":[],"authors":[{"id":466112850,"identity":"4ad0ae95-fb0d-4169-9cee-f86968eaf95b","order_by":0,"name":"Parimal Sarda","email":"","orcid":"","institution":"Hemato-Oncology Clinic (HOC), Vedanta","correspondingAuthor":false,"prefix":"","firstName":"Parimal","middleName":"","lastName":"Sarda","suffix":""},{"id":466112852,"identity":"eddffb2e-0f79-4e93-a21e-40e9055cce51","order_by":1,"name":"Himil Parikh","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAAzUlEQVRIiWNgGAWjYDCCAxCSh4GZufEBkMXDR4QWxgaIFsZmA5AWNmK1AFmMbRIgAYJa+I43P3/wcc8dGd12xrbKrzl2MmwMzA8f3cCjRfLMMcPGGc+e8ZgdZmy7LbstGegwNmPjHDxaDG7kMDbzHDgM0SK5jRmohYdNmmgtxZLb6knUwvhx22HCWkB+mTkDoqVZmnHbcR42ZgJ+AYbYgw8fDhy2Nzt/+ODHn9uq7fnZmx8+xqcFBTDzgElilYMA4w9SVI+CUTAKRsGIAQC75EzsMe1JvgAAAABJRU5ErkJggg==","orcid":"","institution":"Hemato-Oncology Clinic (HOC), Vedanta","correspondingAuthor":true,"prefix":"","firstName":"Himil","middleName":"","lastName":"Parikh","suffix":""},{"id":466112854,"identity":"078ef61c-77c0-4041-87ba-fe108a6fb8d8","order_by":2,"name":"Sandip Shah","email":"","orcid":"","institution":"Hemato-Oncology Clinic (HOC), Vedanta","correspondingAuthor":false,"prefix":"","firstName":"Sandip","middleName":"","lastName":"Shah","suffix":""}],"badges":[],"createdAt":"2025-05-26 14:38:17","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-6751831/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-6751831/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":84218835,"identity":"254e62f8-95e8-49b7-9f5f-6f796cd7140d","added_by":"auto","created_at":"2025-06-09 11:19:15","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":430282,"visible":true,"origin":"","legend":"\u003cp\u003e(a) shows peripheral eosinophils, including numerous degranulated forms, at 100× magnification [Jenner-Giemsa stain]. No circulating blasts were identified. Panel (b) displays a bone marrow biopsy section at 4× magnification, showing absent fat spaces. Panel (c), captured at 40× magnification, highlights eosinophilic predominance along with interstitial infiltration by immature cells. Finally, the digitally zoomed image of 40x magnification (d) (2×) demonstrates large immature cells with prominent nucleoli located adjacent to the bony trabeculae.\u003c/p\u003e","description":"","filename":"1.png","url":"https://assets-eu.researchsquare.com/files/rs-6751831/v1/6c3412400c1724be43a3ee87.png"},{"id":84220214,"identity":"d22da790-1289-45ed-ab66-856879e6ba36","added_by":"auto","created_at":"2025-06-09 11:27:15","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":678523,"visible":true,"origin":"","legend":"\u003cp\u003eShowsimmunophenotypic profile of the immature cells, as assessed by immunohistochemistry, demonstrated positivity for TdT, PAX5, CD79a, CD10, and CD34. The blasts were negative for CD117, CD3, and CD5. CD20 expression was also absent (not shown). Representative areas of the biopsy were selected for illustration.\u003c/p\u003e","description":"","filename":"2.png","url":"https://assets-eu.researchsquare.com/files/rs-6751831/v1/f4f30de7b75eee6c04d4721d.png"},{"id":84220216,"identity":"4fbf8876-81b8-4a0a-943b-c90ad14d6a59","added_by":"auto","created_at":"2025-06-09 11:27:20","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":1395619,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-6751831/v1/e89b9bd6-b040-455c-b3b8-08f46e9a13ee.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"Masked by Eosinophils: A Cryptic Presentation of Paediatric B-ALL with IGH::IL3 Rearrangement","fulltext":[{"header":"Introduction","content":"\u003cp\u003eHypereosinophilia (HE) is uncommon in children and is typically associated with allergic, parasitic, or autoimmune disorders. Rarely\u0026mdash;accounting for less than 1% of cases\u0026mdash;it may precede or accompany hematologic malignancies such as acute lymphoblastic leukemia (ALL). One such rare entity is B-ALL with IGH::IL3 rearrangement [formerly known as \u003cem\u003et(5;14)\u003c/em\u003e], a World Health Organization (WHO)-recognized subtype characterized by interleukin-3 overproduction leading to marked eosinophilia, often without circulating blasts.[\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e]\u003c/p\u003e \u003cp\u003eDespite HE being a feature of numerous conditions, including neoplasms, the presence of more common causes often diverts attention from underlying hematologic malignancies, delaying diagnosis and treatment. Furthermore, IGH rearrangements can be cryptic and may escape detection on conventional karyotyping. They are also frequently absent from standard next-generation sequencing (NGS) panels used for leukemia or lymphoma workups.\u003c/p\u003e"},{"header":"Case Presentation","content":"\u003cp\u003eA 6\u0026frac12;-year-old female (height 109 cm, weight 16.5 kg, BMI 13.89) presented with the complaints of abdominal pain, fever, and burning, itchy rashes over the palms and soles for 5\u0026ndash;7 days. On examination, patient did not have any enlarged lymph nodes. The abdomen was soft without any guarding or rigidity and had no palpable hepatosplenomegaly.\u003c/p\u003e \u003cp\u003eA routine complete blood count (CBC) showed leukocytosis with WBC count of 204 \u0026times; 10\u003csup\u003e9\u003c/sup\u003e/L, Hb 11.1 g/dL, and platelet count of 187 x 10\u003csup\u003e9\u003c/sup\u003e/L. Eosinophils constituted 80% of the leukocytes with an absolute eosinophil count of 1.63 lakh/\u0026micro;L. There were no circulating blasts noted on the peripheral smear. LDH was notably elevated (788 U/L).\u003c/p\u003e \u003cp\u003eIn view of complaint of abdominal pain, an ultrasound of the abdomen was performed which showed mild ascites and congestive hepatomegaly. Spleen was however normal in size. 2D echocardiography was done as a part of work-up for hypereosinophilia which revealed acute eosinophilic myocarditis with LVEF 50\u0026ndash;55% and a follow-up troponin (TROP-I) was also elevated with the levels of 5339.2 ng/ml.\u003c/p\u003e \u003cp\u003eMagnetic Resonance Imaging (MRI) brain suggested acute/subacute infarcts. An outside marrow aspirate report showed 2% blasts with 55% eosinophils. Megakaryocytes were adequate with normal morphology. However, immunophenotyping by flowcytometry was also done outside which showed\u0026thinsp;~\u0026thinsp;10% suspicious B-lymphoblasts and the overall findings were interpreted as myeloid/lymphoid neoplasm with eosinophilia. Cytogenetics \u0026amp; Next generation sequencing were performed, however all of that turned out to be negative. In view of the above reports, patient was started on Hydroxyurea \u0026amp; Naproxen.\u003c/p\u003e \u003cp\u003eWe received this case for review at our centre where we confirmed peripheral blood eosinophilia with ~\u0026thinsp;91% eosinophils and no circulating blasts. The total count was now 149 x 10\u003csup\u003e9\u003c/sup\u003e/L (probably due to hydroxyurea therapy) with the differential count showing neutrophils- 01%, lymphocytes- 03%, monocytes- 01%, basophils- 03% and eosinophils- 91%. The absolute eosinophil count was 135 x 10\u003csup\u003e9\u003c/sup\u003e/L. We did not receive bone marrow aspirate and hence were not able to review the same at our end. The bone marrow biopsy for review was hypercellular (~\u0026thinsp;100%) with interstitial immature precursors along with hyperplasia of the eosinophils and their precursors as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e. We went ahead with the immunohistochemistry panel as represented in Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e, which showed that the blasts were positive for CD10, PAX5, CD79a, TdT, CD34 constituting\u0026thinsp;~\u0026thinsp;35\u0026ndash;40% of total cellularity while being negative for CD3, CD5, CD117 and CD20 (not shown). Hence the final diagnosis we gave was in favour of B-Acute lymphoblastic leukemia (B-ALL). B-ALL with hypereosinophilia showing an IGH gene rearrangement is a recurrent cytogenetic abnormality mentioned as separate entity in WHO classification of haematolymphoid neoplasms.\u003c/p\u003e \u003cp\u003eWe therefore reviewed the cytogenetics \u0026amp; NGS data and found that IGH::IL3 fusion/rearrangement was not included in the FISH \u0026amp; NGS panels and hence was ordered from our side using a break-apart FISH for IGH as IL3 probe was not available in our region. IGH break-apart FISH was performed on heparinized bone marrow aspirate and turned out to be positive in ~\u0026thinsp;7% cells. As the burden of blasts was very low in the bone marrow aspirate (~\u0026thinsp;10% on immunophenotyping by flowcytometry), this explained the low percent positivity on FISH and was considered to be a cryptic IGH rearrangement likely an IGH::IL3 fusion resulting in this marked eosinophilia causing organ involvement.\u003c/p\u003e "},{"header":"Discussion","content":"\u003cp\u003eThis case highlights the diagnostic challenge of B-lymphoblastic leukemia (B-ALL) presenting with hypereosinophilia in the absence of circulating blasts. Cryptic IGH::IL3 rearrangements may evade detection by conventional cytogenetics, and standard next-generation sequencing (NGS) panels often lack coverage for such atypical fusions. Thus, heightened clinical and molecular awareness is essential when interpreting negative or inconclusive molecular results. Notably, a 2021 study demonstrated that mate-pair sequencing offers superior sensitivity in detecting IGH::IL3 fusions compared to traditional diagnostic approaches.[\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e]\u003c/p\u003e \u003cp\u003eA comprehensive analysis of 24 patients\u0026mdash;one of the largest series to date\u0026mdash;by Fournier et al. reported a median total leukocyte count of 72 \u0026times; 10⁹/L and a median eosinophil count of 32 \u0026times; 10⁹/L, with peripheral blood blasts ranging from 0 to 37 \u0026times; 10⁹/L. Notably, in 5 of their own 8 cases, no peripheral blasts were detectable.[\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e] In our case, both the total leukocyte count and absolute eosinophil count were higher than their cohort, yet, consistent with the majority of their findings, circulating blasts were absent. This observation is diagnostically significant: it underscores the need for a low threshold of suspicion for hematologic neoplasms, especially when peripheral blood findings are non-revealing.\u003c/p\u003e \u003cp\u003eThe eosinophilia observed in such cases is likely reactive, driven by aberrant cytokine production\u0026mdash;particularly IL-3\u0026mdash;associated with cryptic IGH::IL3 fusions. This not only explains the marked eosinophilia and potential for organ infiltration but also contributes to a dilutional effect on blast percentages in both peripheral blood and bone marrow, complicating morphological assessment. In our patient, this dilution likely masked the presence of malignant blasts on morphology, particularly challenging in paediatric cases where hematogones can mimic or obscure lymphoblasts.\u003c/p\u003e \u003cp\u003eFlow cytometry played a critical role in our diagnosis, revealing approximately 10% blasts with a B-lymphoblast phenotype, which were morphologically indistinct and may have otherwise been misclassified. Fournier et al. similarly described a case initially misdiagnosed due to negative findings on conventional FISH and karyotyping, later confirmed via NGS to harbor an IGH::IL3 fusion.[\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e] This reinforces the need for including IGH::IL3 probes in targeted NGS panels, especially in paediatric B-ALL with eosinophilia, as timely identification of such fusions can significantly impact prognosis and therapeutic decisions. While most paediatric B-ALL cases carry a favorable prognosis, IGH::IL3-positive leukemias are considered to have intermediate risk according to WHO guidelines. In our case, we were fortunate to detect the IGH rearrangement by FISH despite the low blast burden in the aspirate\u0026mdash;a reminder of the importance of integrating cytogenetic, flow cytometric, and molecular data for accurate diagnosis.\u003c/p\u003e \u003cp\u003eA recent study from the United States examining hypereosinophilia in the paediatric age group emphasized the importance of maintaining a low threshold for investigating hematological malignancies in such patients. Although only one case of acute lymphoblastic leukemia (ALL) was identified among their cohort\u0026mdash;accounting for \u0026lt;\u0026thinsp;1% of total cases[\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e]\u0026mdash;the clinical implications are profound, as early diagnosis can dramatically alter the disease trajectory through timely initiation of appropriate therapy.\u003c/p\u003e \u003cp\u003eSeveral key considerations should be kept in mind when evaluating a paediatric patient with eosinophilia. Hypereosinophilia accompanied by clinical symptoms and biochemical or radiologic signs of organ involvement warrants a high index of suspicion for both clonal eosinophilic syndromes and reactive eosinophilia secondary to an underlying neoplasm. The International Cooperative Group on Eosinophil Disorders (ICOG-EO) has recently revised the definition of persistent eosinophilia by reducing the required duration from 4 weeks to 2 weeks[\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e], acknowledging that significant organ damage may already occur by the 4-week mark, and that earlier intervention is critical.\u003c/p\u003e \u003cp\u003eIn India, where parasitic infections remain endemic, empirical administration of anti-helminthics is a common first-line practice. Consequently, patients may already have received antiparasitic treatment by the time they present to a tertiary centre, even when referred from remote areas. Therefore, in any case where a more ominous underlying process is suspected, bone marrow aspiration and trephine biopsy should not be delayed. While biopsies are sometimes avoided due to perceptions of invasiveness, particularly in paediatric settings, it is essential to recognize their diagnostic value. Flow cytometry relies heavily on aspirate quality and may yield inconclusive results in cases with low blast burden or hypocellular aspirates. In such situations, a trephine biopsy coupled with immunohistochemistry remains indispensable for diagnostic accuracy.\u003c/p\u003e \u003cp\u003eOur case further supports the World Health Organization (WHO) classification of B-ALL with t(5;14)(q31;q32)/IGH::IL3 fusion as a distinct clinicopathologic entity. It demands heightened clinical vigilance and the use of advanced diagnostic platforms\u0026mdash;including flow cytometry, FISH, and NGS\u0026mdash;to ensure timely and accurate diagnosis.\u003c/p\u003e"},{"header":"Conclusion","content":"\u003cp\u003eB-lymphoblastic leukemia (B-ALL) with IGH::IL3 rearrangement represents a rare paediatric subtype that may present with marked hypereosinophilia and little to no circulating blasts. This case highlights the critical importance of comprehensive bone marrow evaluation and the application of advanced molecular diagnostics in atypical presentations. Heightened awareness of this entity is essential to avoid misdiagnosis, ensuring timely initiation of appropriate therapy and potentially improving clinical outcomes.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eAuthor contributions:\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eP.S. contributed to the conceptualisation, manuscript drafting and writing, analysis of histopathological and immunohistochemical data. Additionally, P.S. was involved in the interpretation of cytogenetics and molecular data, as well as the review and editing of the manuscript.\u003c/p\u003e\n\u003cp\u003eH.P. contributed to the conceptualization, drafting, and writing of the manuscript, conducted histopathological and immunohistochemical analysis, prepared figures and imaging, and participated in the review and editing of the manuscript.\u003c/p\u003e\n\u003cp\u003eS.S. provided clinical supervision, contributed to the conceptualization, and participated in the review and editing of the manuscript.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eFunding disclosure:\u0026nbsp;\u003c/strong\u003eThis study was not supported by any funding.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eConflicts of interest:\u0026nbsp;\u003c/strong\u003eThe authors declare that they have no conflict of interest.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eEthics approval statement (if applicable):\u003c/strong\u003e Ethical approval was not required for this case report as this case was derived retrospectively and none of the patient\u0026rsquo;s identification has been revealed. Written informed consent was obtained from the patient for the publication of this report and any accompanying images.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003ePatient consent statement (if applicable):\u0026nbsp;\u003c/strong\u003eWritten informed consent was obtained from the parents.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eConsent for publication:\u003c/strong\u003e Consent for publication was obtained from the parents.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eFournier B, Balducci E, Duployez N et al (2019) B-ALL With t(5;14)(q31;q32); IGH-IL3 Rearrangement and Eosinophilia: A Comprehensive Analysis of a Peculiar IGH-Rearranged B-ALL. Front Oncol 9:1374\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eGuenzel AJ, Smadbeck JB, Golden CL et al (2021) Clinical utility of next generation sequencing to detect IGH/IL3 rearrangements [t(5;14)(q31.1;q32.1)] in B-lymphoblastic leukemia/lymphoma. Ann Diagn Pathol 53:151761\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eNess TE, Erickson TA, Diaz V et al (2023) Pediatric Eosinophilia: A Review and Multiyear Investigation into Etiologies. J Pediatr 253:232\u0026ndash;237e1\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eValent P, Klion AD, Roufosse F et al (2023) Proposed refined diagnostic criteria and classification of eosinophil disorders and related syndromes. Allergy 78:47\u0026ndash;59\u003c/span\u003e\u003c/li\u003e\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":true,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"journal-of-hematopathology","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"","sideBox":"Learn more about [Journal of Hematopathology](https://link.springer.com/journal/12308)","snPcode":"12308","submissionUrl":"https://submission.springernature.com/new-submission/12308/3","title":"Journal of Hematopathology","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"stoa","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false},"keywords":"","lastPublishedDoi":"10.21203/rs.3.rs-6751831/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-6751831/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eHypereosinophilia is uncommon in the paediatric population and may be associated with either primary or secondary conditions. In a very small proportion of cases (less than 1%), it forms part of the initial presentation of acute lymphoblastic leukemia (ALL). More frequently, hypereosinophilia appears before overt leukemia symptoms develop, which can delay diagnosis and place affected children at increased risk due to the lack of early intervention.\u003c/p\u003e \u003cp\u003eWe recently reviewed a case of 6\u0026frac12;-year-old female who presented with hypereosinophilia and no circulating blasts. Bone marrow showed significant prominence of eosinophils and their precursors with ~\u0026thinsp;2% blasts on morphology. Bone marrow biopsy was received for review and showed a significant burden of immature cells/blasts which on immunohistochemistry was revealed as B-acute lymphoblastic leukemia (B-ALL). Cytogenetics by Fluorescence in-situ hybridization (FISH) showed IGH rearrangement while the routine karyotyping as well as Next Generation Sequencing (NGS) were both negative for any genetic aberrancy. This case highlights the importance of a thorough marrow evaluation in paediatric eosinophilia and discusses the challenges in identifying cryptic rearrangements that are not evident on standard cytogenetic and molecular panels.\u003c/p\u003e","manuscriptTitle":"Masked by Eosinophils: A Cryptic Presentation of Paediatric B-ALL with IGH::IL3 Rearrangement","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-06-09 11:19:11","doi":"10.21203/rs.3.rs-6751831/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"decision","content":"Revision requested","date":"2025-06-17T11:49:02+00:00","index":"","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2025-06-16T19:35:20+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2025-06-06T00:04:50+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"134637585076411572038672546528271986085","date":"2025-06-04T00:49:58+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"225372626615975552962126144642482194920","date":"2025-06-03T15:08:43+00:00","index":"hide","fulltext":""},{"type":"reviewersInvited","content":"","date":"2025-06-03T05:19:43+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2025-06-02T12:01:18+00:00","index":"","fulltext":""},{"type":"checksComplete","content":"","date":"2025-06-02T11:57:25+00:00","index":"","fulltext":""},{"type":"submitted","content":"Journal of Hematopathology","date":"2025-05-26T14:32:10+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"journal-of-hematopathology","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"","sideBox":"Learn more about [Journal of Hematopathology](https://link.springer.com/journal/12308)","snPcode":"12308","submissionUrl":"https://submission.springernature.com/new-submission/12308/3","title":"Journal of Hematopathology","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"stoa","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false}}],"origin":"","ownerIdentity":"a6b3b8d0-8016-4ecc-adb9-403357912347","owner":[],"postedDate":"June 9th, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"under-review","subjectAreas":[],"tags":[],"updatedAt":"2025-07-03T13:53:28+00:00","versionOfRecord":[],"versionCreatedAt":"2025-06-09 11:19:11","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-6751831","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-6751831","identity":"rs-6751831","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}