RPS6 and neoplasm with perivascular epithelioid cell differentiation: 10 In addition, PEComas often show evidence of mTORC1 activation with phosphorylation of p70S6K and ribosomal protein S6 by immunohistochemistry (IHC).11 Aberrant mTORC1 signaling is a key driver of cell proliferation and tumor formation,12 suggesting that mTORC1 inhibition may be a promising therapeutic approach for PEComas.