PTEN and nonpapillary renal cell carcinoma: To begin to address the hypothesis that the chemotherapy resistance of PTEN-deficient RCC may be due to p21 induction, we asked whether cisplatin increases p21 in ACHN cells (a PTEN-wt ccRCC cell line) and whether this increase is antagonized by mTOR inhibition (which has been shown to have antitumor activity).