Cigarette smoking in relation to risk of ductal carcinoma in situ of the breast in a cohort of postmenopausal women.

In numerous studies, investigators have examined the association of active smoking with risk of invasive breast cancer, but to the authors' knowledge, no cohort study has assessed smoking in relation to the risk of in situ breast cancer, the postulated penultimate stage preceding invasive breast cancer. The authors examined the latter association using data collected at baseline from 63,393 women in the Women's Health Initiative Clinical Trial. A total of 486 cases of ductal carcinoma in situ (DCIS) of the breast were identified during 8 years of follow-up between 1993 and 2005. Cox proportional hazards models were used to estimate hazard ratios and 95% confidence intervals. For the primary analysis, invasive breast cancer was treated as a competing risk. After adjustment for covariates, associations with smoking status, smoking intensity, duration, pack-years, and age at quitting were all close to the null value and showed few meaningful trends. Sensitivity analyses performed to address different possibilities with respect to the natural history of breast cancer also did not provide consistent evidence of an association of smoking with DCIS. The results of this large cohort study provide little support for an association of cigarette smoking with risk of DCIS in postmenopausal women.