Data from FET-Rearranged Myoepithelial Tumors Are Clinically Heterogeneous and Epigenetically Distinct from PLAG1-Rearranged Adnexal and Salivary Gland Myoepithelial Tumors

AbstractPurpose: Fusion-positive myoepithelial tumors (MET) are clinicopathologically heterogeneous and variably termed mixed tumors and myoepithelial carcinomas. As FET-rearranged METs lack ductal/epithelial differentiation, we test whether FET-rearranged METs are epigenetically distinct from adnexal PLAG1-rearranged METs, which we hypothesize to be analogues of salivary gland METs. Experimental Design: DNA methylation profiling from a multi-institutional cohort of 52 fusion-positive skin, soft-tissue, and bone MET cases was performed and compared with diverse tumor types, including salivary METs. The MET subgroups harbored EWSR1::KLF15, EWSR1/FUS::KLF17, EWSR1::PBX1, EWSR1::PBX3, EWSR1/FUS::POU5F1, SS18::POU5F1, EWSR1::ZNF444, and PLAG1 rearrangements. Pooled clinicopathologic and outcome analysis with new and published cases (total 185) was performed. Results: The MET subgroups showed significant heterogeneity in age, site, and histology. Specifically, EWSR1::KLF15 METs affected predominantly young children (