Background: Information is limited on the risk of contralateral breast cancer after a diagnosis of breast carcinoma in situ (BCIS).
Methods: In western Washington, between 1974 and 1993, 1929 women with a first primary ductal carcinoma in situ (DCIS) and 282 women with a first primary lobular carcinoma in situ (LCIS) were followed for contralateral breast cancer. Rates of contralateral invasive breast cancer and BCIS were compared with population rates of first primary breast cancer using Poisson regression to adjust for age and calendar year.
Results: The rate of contralateral invasive disease after BCIS was approximately twice the population rate for women with DCIS and three times the population rate for women with LCIS; relative rates decreased somewhat with increasing time since diagnosis of LCIS, but were fairly stable after DCIS. The relative rate of contralateral DCIS after BCIS was substantially higher than for contralateral invasive disease, but dropped dramatically after the first year after the initial BCIS, especially among women with LCIS. Contralateral BCIS usually was of the same histologic type as the initial BCIS; histologic concordance of BCIS was 71% for women with an initial LCIS and 78% for women with DCIS.
Conclusions: Data suggest that the rate of contralateral invasive breast cancer is elevated for at least 5 years after a diagnosis of BCIS compared with the rate of first primary breast cancer in the population, and that the rate is only slightly higher for women with LCIS than for women with DCIS. The markedly elevated rate of contralateral DCIS may result in large part from increased medical surveillance of women diagnosed with BCIS, especially during the first year after the initial diagnosis.