ABCG2 and cancer: The polymorphisms of G34A and C421A in the ABCG2 gene have been reported to alter the expression or activity of ABCG2 [15, 17, 27, 28] and predispose carriers to a high risk of developing cancers such as nonpapillary renal cell carcinoma [18], DLBCL [21], and hormone-refractory prostate cancer [19].