Update on the management of BCOR::CCNB3 sarcoma.

Abstract

BCOR::CCNB3 sarcoma is a rare sarcoma defined by the BCOR::CCNB3 fusion gene. It predominantly affects males under 20, with a slight predominance of bone origin. Initially grouped as 'Ewing-like,' it is now a distinct entity, a major part of 'sarcoma with BCOR genetic alterations.' Incidence is low, estimated at under 10 annual cases in Japan. Radiologically, it can mimic other high-grade sarcomas, with variable lytic or sclerotic bone lesions and nonspecific soft tissue findings. By contrast, it sometimes appears well-defined and benign-like. Pathologically, the detection of BCOR::CCNB3 fusion is key to diagnosis. Histology varies from small round cells to spindle cells, showing CD99, BCOR, Cyclin D1, and SATB2 positivity, with CCNB3 differentiating it from BCOR-ITD. Molecular testing confirms the diagnosis. Treatment involves wide resection and chemotherapy, with the Ewing sarcoma protocol often chosen. Approximately 20% are metastatic at diagnosis, and local recurrence after surgery occurs in as high as ⁓20% of BCOR::CCNB3 sarcomas. The relatively high local recurrence rate is probably because of the infiltrative growth. Complete response to neoadjuvant chemotherapy may indicate a better prognosis. Less frequent metastasis at diagnosis indicates that this sarcoma is less aggressive than Ewing sarcoma. Five-year overall survival is ⁓75%, but the prognosis of non-resectable or metastatic cases is worse. Further research is crucial for tailored treatment. Due to the tumor's super-rarity, collaborative, multi-institutional studies are essential, allowing for robust clinical trials and outcome analyses. Long-term follow-up studies are also necessary to assess late effects and survival.