Two criteria suggest that primary multidrug resistance in human adenocarcinomas of the kidney results, at least in part, from expression of the mdr1 gene: (1) mdr1 mRNA levels are elevated in four unselected kidney adenocarcinoma cell lines that show a multidrug-resistant phenotype; and (2) multidrug resistance in these kidney cancer cell lines is reversed by verapamil and quinidine, agents known to reverse mdr1-associated drug resistance in cell lines selected for multidrug resistance in vitro.
In summary, this meta-analysis suggests that the MDR1C3435T polymorphism is associated with cancer susceptibility, increasing the risk of breast and renal cancer.