For CTLA-4 -1661 A/G polymorphism, the results showed that the CTLA-4 -1661A/G polymorphism was significantly associated with an increased cancer risk (GA vs. AA: OR = 1.44, 95%CI = 1.13–1.82; GA+GG vs. AA: OR = 1.35, 95%CI = 1.07–1.69; G vs. A: OR = 1.21, 95%CI = 1.01–1.47), especially in gastric cancer, breast cancer, other cancers and in Asians population subgroups. This evidence concerns the gene CTLA4 and breast cancer.