ABCB1 and renal cell carcinoma: Extensive studies with complete follow-up detailing expression of MDR-1 P-gp and MRP-1 together with further MDR associated markers (including LRP and MRP family members) and associated proteins may help to fully elucidate the specific contributions of these efflux pumps to the chemoresistance of RCC and furthermore address any possible prognostic and/or predictive role.