The heterozygous CYP1B1 (Val/Leu) genotype was associated with a significant increased risk of breast cancer (Odds ratio [OR] = 1.59, 95% Confidence Interval [CI] 1.01–2.52), compared with the homozygous wild type CYP1B1 (Val/Val) genotype. The gene discussed is CYP1B1; the disease is breast carcinoma.