Ductal carcinoma in situ and cause-specific mortality among younger and older postmenopausal women: the Women's Health Initiative.

Background: Whether DCIS is associated with higher breast cancer-specific and all-cause mortality is unclear with few studies in older women. Therefore, we examined DCIS and breast cancer-specific, cardiovascular (CVD)-specific, and all-cause mortality among Women's Health Initiative (WHI) Clinical Trial participants overall and by age (< 70 versus ≥ 70 years).

Methods: Of 68,132 WHI participants, included were 781 postmenopausal women with incident DCIS and 781 matched controls. Serial screening mammography was mandated with high adherence. DCIS cases were confirmed by central medical record review. Adjusted multivariable Cox proportional hazard regression models were used to estimate hazard ratios (HRs) and 95% confidence intervals (CI). Kaplan Meier (KM) plots were used to assess 10-year and 20-year mortality rates.

Results: After 20.3 years total, and 13.2 years median post-diagnosis follow-up, compared to controls, DCIS was associated with higher breast cancer-specific mortality (HR 3.29; CI = 1.32-8.22, P = 0.01). The absolute difference in 20-year breast cancer mortality was 1.2% without DCIS and 3.4% after DCIS, log-rank P = 0.026. Findings were similar by age (< 70 versus ≥ 70 years) with no interaction (P interaction = 0.80). Incident DCIS was not associated with CVD-specific mortality (HR 0.77; CI-0.54-1.09, P = 0.14) or with all-cause mortality (HR 0.96; CI = 0.80-1.16, P = 0.68) with similar findings by age.

Conclusions: In postmenopausal women, incident DCIS was associated with over three-fold higher breast cancer-specific mortality, with similar findings in younger and older postmenopausal women. These finding suggest caution in using age to adjust DCIS clinical management or research strategies.