Important Recently Characterized Non-Ewing Small Round Cell Tumors

Round cell sarcomas morphologically similar to Ewing sarcoma, but lacking the classic immunohistochemical features, EWSR-ETS family fusions, and other signs of differentiation, are classified as Ewing-like sarcomas. Recent molecular advances led to the discovery and characterization of two recurrent oncogenic fusion rearrangements, CIC-DUX4 and BCOR-CCNB3, in a significant subset of Ewing-like sarcomas. Uncovered alternate fusion partners broadened the proposed classification of these tumors to CIC-rearranged sarcomas and BCOR-rearranged sarcomas. This article summarizes the clinicopathologic and molecular features of these entities, with particular attention paid to those features that overlap with and distinguish these sarcomas from other round cell sarcomas.