Purpose: To screen for factors that might predict the risk of developing metachronous contralateral breast cancer (CBC), taking into account the influence of local or distant recurrence, and to assess the annual incidence of CBC.
Patients and methods: Of 4,748 women with invasive unilateral breast cancer, clinical stage I to IIIa, treated between 1981 and 1987, 282 metachronous CBCs were diagnosed. Due to competing risks between the occurrence of CBC and other events, several options for multivariate analysis were considered.
Results: The median follow-up time was 80 months (range, 1 to 158). The cumulative rate of CBC was 4.1% +/- 0.3% at 5 years, and the annual incidence rate of CBC increased slowly, while the risk of local recurrence and metastases decreased after the fourth year. Whichever model we chose, age less than 55 years (relative risk [RR] = 1.40) at the time of diagnosis of the first breast cancer, as well as the presence of lobular type carcinoma (RR = 1.50), was associated with an increased risk of developing a tumor in the contralateral breast. Adjuvant chemotherapy significantly decreased (RR = 0.54) the risk of CBC.
Conclusion: Lobular histology and age less than 55 years are found to increase the risk of CBC, while adjuvant chemotherapy significantly decreased the risk of CBC. The progressive rise in the annual incidence rates of CBC, together with the absence of a link between clinical prognostic factors of the first cancer and CBC, suggested that CBC can be considered as a second primary breast cancer.