BCOR-CCNB3 fusion sarcoma is cyclin B3-positive, usually occurs in bone or soft tissue of children, and may mimic a poorly differentiated synovial sarcoma.
More than 50% of cases stained positive for SATB2 and Pax8, raising the hypothesis of a potential use of these markers in the identification of BCOR-CCNB3 positive undifferentiated/unclassified sarcomas.
We also describe the first adult case of MGA-NUTM1 fusion sarcoma, as well as cartilaginous differentiation in a BCOR-CCNB3 fusion sarcoma, which has not been previously reported.
These results are in keeping with a "BCOR-alteration family" of renal and extrarenal neoplasms which includes CCSK and undifferentiated round cell sarcomas of soft tissue/primitive myxoid mesenchymal tumor of infancy (which typically harbor BCOR internal tandem duplication), and BCOR-CCNB3sarcomas, all of which are primarily driven by BCOR overexpression and have overlapping (but not identical) clinicopathologic features.
Heterogeneous elements included a myxoid spindle cell component in three BCOR-CCNB3 sarcomas and an epithelioid cell component in two CIC-associated sarcomas (one CIC-DUX4-positive and one CIC-DUX4-negative sarcomas).
The spectrum of ELS is now expanding, and additional gene fusion partners besides DUX4 or CCNB3 have been detected, and the terms CIC or BCOR-rearranged sarcomas have recently been proposed.
In conclusion, this study provides a detailed description of the histologic spectrum, immunohistochemical features, and clinical characteristic of BCOR-CCNB3sarcoma justifying distinction from Ewing sarcoma with its typical EWS/FUS-ETS translocations.
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.
Finally, we show that CCNB3 immunohistochemistry is a powerful diagnostic marker for this subgroup of sarcoma and that overexpression of BCOR-CCNB3 or of truncated CCNB3 activates S phase in NIH3T3 cells.