MTOR and renal cell carcinoma: Interestingly, several circulating biomarkers like cytokines, are investigated in RCC patients (63), including IL-6, IL-1 and others; in fact, in RCC, pretreatment concentrations of plasma biomarkers (e.g., cytokines and angiogenic factors) have previously been studied in order to predict the outcome of VEGF or mTOR blocking agents (64).