Updates in keratin-positive mesenchymal neoplasia. (PubMed, Semin Diagn Pathol)
Recent examples include spindle cell rhabdomyosarcomas with TFCP2 fusions, keratin-positive giant-cell rich tumors with HMGA2::NCOR2 fusions, NR1D1- rearranged sarcomas, malignant epithelioid neoplasms with FET::CREB fusions, and the very recently described ossifying spindled and epithelioid tumors (OSET). This review will address the unique clinical, histologic, and immunophenotypic characteristics of these rare neoplasms and provide practical considerations for molecular testing in challenging cases of keratin-positive mesenchymal neoplasia.