Dedifferentiated Osteosarcoma of the Wrist With BCOR Sarcoma Component in a 22-Year-Old Patient: A Case Report.

We report a unique case of a 22-year-old male with a progressively enlarging mass on the right thumb. Initial biopsies suggested a low-grade osteogenic tumor. Following partial amputation, gross examination revealed a well-circumscribed 3.7cm mass involving the metacarpal bone with soft tissue invasion. Histologically, the tumor displayed features of low-grade central osteosarcoma with areas transitioning to a round blue cell morphology resembling Ewing sarcoma. Comprehensive molecular testing-including next-generation sequencing (NGS) and cytogenomic microarray analysis (CMA)-identified amplifications of MDM2 and CDK4, hallmark alterations of low-grade osteosarcoma. Notably, a BCOR internal tandem duplication (ITD) was also detected. The final diagnosis was central low-grade osteosarcoma with dedifferentiation to BCOR-altered sarcoma. To our knowledge, this is the first reported case of osteosarcoma with BCOR sarcoma dedifferentiation occurring in the wrist of a young adult. BCOR ITD sarcomas have previously been described exclusively in nonappendicular soft tissues of infants and young children, without known association with osteosarcoma. This case highlights the diagnostic value of integrating NGS (DNA and RNA) and CMA in sarcomas with mixed or unusual histology. Such tools are essential for precise classification, prognostication, and consideration of targeted therapies in rare and histologically complex bone tumors.