Ko K-P., et al. - The association between the known carcinogen, tobacco, and cancer risk in BRCA mutation carriers has not been determined. Cigarette smoking, reproductive, and medical histories were analyzed. During 26,711 person-years of follow-up, 700 incident cancers were diagnosed. In the current study, cigarette smoking was shown to be associated with increased risks of breast and ovarian cancer in patients with BRCA1 or BRCA2 mutations.