We are therefore of the view that tumors with diffuse myomelanocytic differentiation should be regarded as being related to the PEComa family irrespective of site of origin or desmin positivity, and that it is the characteristic morphology and immunophenotype that warrants separating these tumors from classic leiomyosarcoma that exhibit only muscle differentiation. This evidence concerns the gene DES and neoplasm with perivascular epithelioid cell differentiation.