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.