SSX2 and breast cancer: To investigate the role of wild-type SSX2 in the regulation of PcG protein function, we expressed the protein in SSX-negative cancer cell lines derived from tumor types that frequently express SSX2 (39,42–44), including melanoma (A375; DOX inducible model), breast cancer (MCF7; DOX inducible model), colon cancer (HCT116) and tumorigenic mesenchymal stem cells (hMSC-TERT20; sarcomas may be derived from transformed hMSC (45)).