Other immunohistochemical studies on smaller patient cohorts report 61.5% (8/13) and 47.6% (10/21) of RCC showing MDR-1 P-gp positivity [14,15]; studies investigating MDR-1 gene expression in RCC report varying levels of gene expression, in general slightly less that the MDR-1 P-gp protein expression observed here [19-23]. This evidence concerns the gene ABCB1 and renal cell carcinoma.