BCOR-CCNB3 sarcoma (BCS) is an undifferentiated tumor that has some clinical and morphologic similarity to classic Ewing sarcoma, but it is characterized by a distinct BCOR-CCNB3 gene fusion.
The BCOR-CCNB3 positive sarcoma is a recently identified sarcoma morphologically and clinically similar to Ewing sarcoma in adolescents and young adults.
In contrast to ES, BCS shows consistent BCOR overexpression, and preliminary evidence suggests that these tumors share morphologic features with other tumors harboring BCOR genetic alterations, including BCOR internal tandem duplication (ITD) and BCOR-MAML3.
These tumors were subjected to methylation profiling and could be assigned to Ewing sarcoma in 14 (47%), to small blue round cell tumors with CIC alteration in 6 (20%), to small blue round cell tumors with BCOR alteration in 4 (13%), to synovial sarcoma and to malignant rhabdoid tumor in 2 cases each.
BCOR-CCNB3 sarcoma is a genetically defined undifferentiated malignancy with Ewing sarcoma (ES)-like round cells, and preferentially affects the bones of male adolescents.
In this review we discuss the main categories of undifferentiated round cell sarcoma, in relation to Ewing sarcoma and its molecular variants, with particular emphasis on the genetic and biologic features of recently described entities including desmoplastic small round cell tumor and CIC-DUX4 as well as BCOR-CCNB3-associated round cell sarcomas.