Head and Neck Round Cell Sarcomas: A Comparative Clinicopathologic Analysis of 2 Molecular Subsets: Ewing and CIC-Rearranged Sarcomas.

CIC-rearranged sarcoma (CRS) is a relatively new entity defined by its pathognomonic genetic signature and undifferentiated round cell phenotype, initially grouped together with the 'Ewing sarcoma-like tumors'. However, increasing data suggest that these tumors should be regarded as a stand-alone pathologic entity. We conducted a clinicopathologic analysis on molecularly conformed Ewing sarcoma (ES) and CRS arising in the head and neck (HN) and compared to a well characterized cohort of ES and CRS from other locations. A total of 41 HN round cell sarcoma patients were selected from our institutional and consultation files, including 25 ES (median 20 years) and 16 CRS (median 29 years). Clinical follow-up information was available for all ES patients, ranging from 4 to 436 months (median 70 months), while for CRS, follow-up information was available in 11 patients (69%), ranging from 1 to 269 months (median 27 months). The most common location for ES was the facial and jaw bones (56%), while CRS occurred exclusively in the soft tissue, commonly in the neck. CRS showed variable CD99 staining in 75% of cases and diffuse WT1 (6/6) reactivity, while all ES expressed diffuse membranous staining for CD99 but none for WT1 (0/6). The 2-year overall survival (OS) rate for HN-CRS patients was 78%, while for HN-ES it was 100%. The OS of ES and CRS showed a trend toward a favorable outcome for HN-round cell sarcomas compared to other sites. Our findings suggest that HN-CRS have different clinical presentation and pathologic features compared to ES and should be classified as a stand-alone pathologic entity.