Women with ductal carcinoma in situ (DCIS), or stage 0 breast cancer, often experience a second primary breast cancer (DCIS or invasive), and some ultimately die of breast cancer.

To estimate the 10- and 20-year mortality from breast cancer following a diagnosis of DCIS and to establish whether the mortality rate is influenced by age at diagnosis, ethnicity, and initial treatment received.

Observational study of women who received a diagnosis of DCIS from 1988 to 2011 in the Surveillance, Epidemiology, and End Results (SEER) 18 registries database. Age at diagnosis, race/ethnicity, pathologic features, date of second primary breast cancer, cause of death, and survival were abstracted for 108,196 women. Their risk of dying of breast cancer was compared with that of women in the general population. Cox proportional hazards analysis was performed to estimate the hazard ratio (HR) for death from DCIS by age at diagnosis, clinical features, ethnicity, and treatment.

Ten- and 20-year breast cancer-specific mortality.

Among the 108 196 women with DCIS, the mean (range) age at diagnosis of DCIS was 53.8 (15-69) years and the mean (range) duration of follow-up was 7.5 (0-23.9) years. At 20 years, the breast cancer-specific mortality was 3.3% (95% CI, 3.0%-3.6%) overall and was higher for women who received a diagnosis before age 35 years compared with older women (7.8% vs 3.2%; HR, 2.58 [95% CI, 1.85-3.60]; P < .001) and for blacks compared with non-Hispanic whites (7.0% vs 3.0%; HR, 2.55 [95% CI, 2.17-3.01]; P < .001). The risk of dying of breast cancer increased after experience of an ipsilateral invasive breast cancer (HR, 18.1 [95% CI, 14.0-23.6]; P < .001). A total of 517 patients died of breast cancer following a DCIS diagnosis (mean follow-up, 7.5 [range, 0-23.9] years) without experiencing an in-breast invasive cancer prior to death. Among patients who received lumpectomy, radiotherapy was associated with a reduction in the risk of ipsilateral invasive recurrence at 10 years (2.5% vs 4.9%; adjusted HR, 0.47 [95% CI, 0.42-0.53]; P < .001) but not of breast cancer-specific mortality at 10 years (0.8% vs 0.9%; HR, 0.86 [95% CI, 0.67-1.10]; P = .22).

Important risk factors for death from breast cancer following a DCIS diagnosis include age at diagnosis and black ethnicity. The risk of death increases after a diagnosis of an ipsilateral second primary invasive breast cancer, but prevention of these recurrences by radiotherapy does not diminish breast cancer mortality at 10 years.