Clinicopathologic features and contralateral breast cancer risk in BRCA1/2 pathogenic variant carriers: a multicenter registry study of Japanese women.

This large-scale study presents the clinicopathological characteristics and cumulative incidence of contralateral breast cancer (CBC) in Japanese BRCA1/2 pathogenic variant carriers, including cases diagnosed after the implementation of national insurance coverage. We analyzed 2949 breast cancer cases from the registry database of the Japanese Organization of Hereditary Breast and Ovarian Cancer. BRCA1 carriers predominantly developed triple-negative breast cancer, whereas BRCA2 carriers more frequently developed luminal-type tumors, with a younger age of onset observed in BRCA1 carriers. No significant clinicopathological differences were found between the age groups. The cumulative incidence of CBC was 10.0% at five years and 29.0% at 10 years among BRCA1 carriers and 14.0% at five years and 19.0% at 10 years among BRCA2 carriers. CBC was observed in all age groups, including older patients. These findings highlight the importance of individualized decision-making in surgical planning and surveillance strategies. This study included a broad age range of patients, reflecting real-world data following the expansion of insurance coverage in Japan. Further case studies and long-term follow-up are warranted. Our findings support the development of appropriate clinical care and preventive strategies for BRCA1/2 carriers in Japan.