Undifferentiated Small Round Cell Sarcomas of Bone.

Undifferentiated small round cell sarcomas are a heterogeneous group of high-grade sarcomas of uncertain histogenesis. In this review, the key clinicopathological, immunohistochemical, and molecular characteristics of select entities that commonly originate from bones (ie, Ewing sarcoma, BCOR::CCNB3 sarcoma, and EWSR1::NFATC2 sarcomas) are summarized. CIC-rearranged sarcomas are briefly discussed because they rarely arise from bone. Relevant immunohistochemical markers, differential diagnoses, and practical pitfalls are also reviewed.