HEY1 and mesenchymal chondrosarcoma: Whereas some tumor types are characterized by highly specific gene fusions, e.g., mesenchymal chondrosarcoma (HEY1::NCOA2), others show a wider spectrum of rearrangements, some of which form fusions between members of distinct gene families, e.g., Ewing sarcoma (FET::ETS fusions) or between recurrent genes / gene family members and a variety of fusion partners, e.g., myoepithelial tumors (EWSR1 with POU5F1, PBX1, PBX3, or ZNF444).