Using breast cancer mouse models, different radiation fractionation schemes (20 Gy × 1, 8 Gy × 3, or 6 Gy × 5 fractions in consecutive days) were tested in combination with the immune checkpoint inhibitor, anti-CTLA-4 antibody, by examining two tumor sites, a primary site that was irradiated and a secondary site that was unirradiated [26]. This evidence concerns the gene CTLA4 and breast cancer.