ERBB2/ERBB3-mutated S100/SOX10-positive uterine sarcoma: something new.

A distinctive subset of uterine mesenchymal tumors display recurrent genetic fusions involving receptor tyrosine kinases, including NTRK, PDGFB, FGFR1, and RET, presumably leading to aberrant pathway activation. A pair of recent studies have highlighted the existence of a genetic fusion-negative uterine sarcoma that is characterized by activating mutations in ERBB2/ERBB3, CDKN2A deletion, inactivating ATRX mutation, and a S100 + /SOX10 + immunohistochemical profile. This report describes another case of this emerging entity that was diagnosed in a 57-year-old woman. The 8-cm tumor was centered in the uterine cervix and was comprised mostly of spindle cells configured in fascicles. The tumor was diffusely immunoreactive for SOX10 and S100, with more localized staining for CD68, CD56, MITF, and PRAME. HMB-45, ER, PR, HER2, Melan-A/MART1, STAT6, pan-TRK, ALK, CD34, desmin, CD10, myogenin, and pancytokeratins were all negative, and there was retained expression of H3K27me3. The following molecular alterations were found: ERBB2 p.Val777Leu, ATRX p.F2113Sfs*, CDKN2A deep deletion, NF1 p.W2317*, SMARCA4 p691Sfs*. The authors review the sparse literature on molecular-genetic aberrations involving the epidermal growth factor receptor family of receptor tyrosine kinases (ERBB1/EGFR, ERBB2, ERBB3, and ERBB4) in uterine mesenchymal tumors, a review that suggests that such tumors may be pathologically heterogeneous. The potential clinical significance of demonstrating a targetable ERBB2/ERBB3 tyrosine kinase mutation or other EGFR family aberrations, as well as its distinctive pathologic profile, supports the segregation of the tumor reported herein as a distinct and emerging entity.