Our previous studies showed that single nucleotide polymorphisms (SNPs) in ATP-binding cassette, sub-family B (MDR1 or ABCB1), X-ray repair cross-complementing group 1 (XRCC1) and ATP-binding cassette sub-family G member 2 (ABCG2) might be probable risk factors for chronic lymphocytic leukemia (CLL), breast cancer and chronic myeloid leukemia (CML) (Maroofi et al., 2015[22]; Ghafouri et al., 2016[10]; Jalali et al., 2016[15]; Salimizand et al., 2016[26]). The gene discussed is ABCG2; the disease is breast cancer.