RPS6KB1 and renal cell carcinoma: The differences between p-4EBP1 and p-S6K expression found in Xp11.2 RCC patients may be an indication that p-4EBP1 could be phosphorylated by other pathways15, 27 or that mTOR phosphorylates 4EBP1 more actively in Xp11.2 RCC.