SMAD4 and breast cancer: SMAD4 rs12456284:A>G increased BC risk in G-allele carriers (A/G + G/G) in cases with ≥2 BC/OC cases and early-onset cases (OR = 1.2 [95% CI 1.0–1.6] p = 0.04 and OR = 1.4 [95% CI 1.0–1.9] p = 0.03, respectively).