However, the significant impact of gene–gene interaction on BC risk was confirmed only in case of GSTP1 and GSTT1 genetic polymorphisms (P heterogeneity = 0.01) with reduced BC risk for GSTT1 null and GSTP1 Ile105Val + Val105Val combined genotype (OR 0.24, 95 % CI 0.11–0.51; P < 0.0001) (Table 4). The gene discussed is GSTP1; the disease is breast cancer.