Twenty-year incidence and patterns of contralateral breast cancer after breast conservation treatment with radiation

Purpose: This study was undertaken to determine the incidence of contralateral breast cancer (CLB) after treatment for early-stage breast cancer with breast-conserving treatment (BCT), and to observe patterns of CLB presentation.

Methods: Medical records of 1,801 women treated for unilateral AJCC Stage 0–II breast cancer with BCT between 1977 and 2000 were analyzed as a retrospective cohort.

Results: The incidence of any CLB at 20 years was 15.4%. The annual risk of developing any CLB remained constant at approximately 0.75% per year after treatment. The median time to any CLB was 8.2 years (range, 0.5–26.5 years). No difference in incidence of CLB was demonstrated in patients with primary invasive carcinoma vs. DCIS (p = 0.84). The majority of patients (83%) developing CLB tumors developed invasive disease. The risk of developing an invasive CLB did not differ significantly for patients with DCIS vs. those with primary invasive carcinoma (p = 0.20). The method of detection of the primary tumor (mammography vs. physical examination) was not predictive of detection of the CLB (p = 0.20). Finally, the location of CLB tumors was not affected by that of prior tumors (p = 0.82).

Conclusions: The risk of development of CLB persists for at least 20 years after treatment for early-stage breast cancer. CLB tumors are frequently invasive, and their location is not influenced by location of prior tumors. Mammography and physical examination remain essential after BCT for detection of a contralateral breast cancer, regardless of the method of detection of the primary tumor.

Keywords: Breast-conservation treatment, Contralateral breast cancer, Ductal carcinoma in situ, DCIS, Radiation treatment