The presence of the TFE3 fusion protein most likely replaces MiTF in these PEComas, explaining the absence of MiTF expression and the reduced expression of Melan A. TFE3 rearrangements and TSC1/2 changes were previously thought to be mutually incompatible, but a recent report of a TCS1-mutated PEComa with a TFE3-altered phenotype calls this conclusion into question (13). This evidence concerns the gene TSC1 and neoplasm with perivascular epithelioid cell differentiation.