Key result
Immunohistochemistry and molecular genetics are essential for diagnosing pediatric small round cell tumors with overlapping histology.
Why the study?
Small round cell tumors often exhibit overlapping clinical, radiologic, histologic, and immunophenotypic features despite distinct prognostic outcomes, making accurate diagnosis and subclassification reliant on molecular confirmation.
This review highlights the critical role of combining immunohistochemistry and molecular genetic investigations for the accurate diagnosis and subclassification of small round cell tumors in pediatric and young adult patients.
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Should be standard in diagnostic evaluation of pediatric small round cell tumors; extends accuracy of subclassification for research and therapy selection.
Small round cell tumors (SRCT) affecting soft tissue and bone are a distinct category of malignancies. These lesions frequently exhibit similar clinical and radiologic features, may harbor overlapping histologic and immunophenotypic features, and generally have distinct prognostic outcomes. Therefore, in some instances, the diagnosis and accurate subclassification require molecular confirmation. We aimed to provide a comprehensive overview of the morphologic, immunohistochemical, and molecular features of SRCTs of soft tissue and bone in pediatric and young adult patients, with an emphasis on both commonly encountered tumors and rare, recently described entities, accompanied by illustrative material from our TruSight platform. The literature data were mined from the PubMed/Medline, Scopus, and Cochrane databases covering the period from January 1, 2014, to December 31, 2024, and the authors' personal experience with diagnostic cases at their institutions. We reviewed tumors that include sarcoma with EWSR1-non-ETS fusion, CIC-rearranged sarcoma, BCOR-rearranged sarcoma, Ewing sarcoma, alveolar rhabdomyosarcoma, desmoplastic small round cell tumor, high-grade/round cell myxoid liposarcoma, poorly differentiated synovial sarcoma, small-cell type osteosarcoma, mesenchymal chondrosarcoma, and extraskeletal myxoid chondrosarcoma. Immunohistochemistry plays a crucial role in interpreting a specific diagnosis or narrowing the differential diagnosis of SRCTs. Molecular genetic investigations are essential, particularly in cases exhibiting atypical or overlapping histologic and immunohistological features.
Nagy et al. (2026) studied this question. Immunohistochemistry and molecular genetic investigations are essential for accurately diagnosing pediatric small round cell tumors, particularly when histologic features overlap.
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