TSC1 and neoplasm with perivascular epithelioid cell differentiation: Although not well established in PEComa, the known mechanisms of resistance to mTOR inhibitors in other tumors include the activation of the PI3K/AKT or MAPK/ERK pathways, mutation in the kinase domains of TSC1/TSC2, overexpression of ABC transporters, MET activation, or microenvironment changes.