Background: Women diagnosed with breast carcinoma in situ are at increased risk for developing a contralateral breast cancer. The magnitude of this risk and the relationship between this risk and age, time since diagnosis, histologic subtype, and treatment for the first breast cancer is continuing to be defined.
Methods: The risk of developing a contralateral breast cancer is examined among 4198 women diagnosed with breast carcinoma in situ and reported to the Connecticut Tumor Registry (CTR) between January 1, 1975 and March 14, 1998 using Kaplan-Meier estimation. A Cox proportional hazards model is used to assess the effect of surgical treatment, radiation therapy, age at diagnosis, race, histology, marital status, anatomic location within the breast, and time since diagnosis upon this risk.
Results: The cumulative 5- and 10-year probabilities of being diagnosed with a contralateral breast cancer among women initially diagnosed with a ductal breast carcinoma in situ (DCIS) were 4.3% (95% confidence interval, 3.6-5.0%) and 6.8% (95% confidence interval, 5.5-8.2%), respectively. These risks are 3.35 times greater than those for women without a history of breast cancer but are similar to those for women diagnosed with non-metastatic invasive ductal carcinomas of the breast. The cumulative 5- and 10-year probabilities of being diagnosed with a contralateral breast cancer among women initially diagnosed with a lobular breast carcinoma in situ (LCIS) were 11.9% (95% confidence interval, 9.5-14.3%) and 13.9% (95% confidence interval, 11.0-16.8%), respectively.
Conclusions: Women diagnosed with LCIS were 2.6 (95% confidence interval, 2.0-3.4%) times more likely than women with DCIS to be diagnosed with a contralateral breast cancer within the first six months of the first breast primary. The risk of developing a contralateral breast cancer more than 6 months after the initial breast cancer was independent of surgical or radiation therapy, time since diagnosis, age at diagnosis, histology, race, marital status, or anatomic location of the cancer within the breast.