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

Purpose: 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.

Methods: We analyzed 2949 breast cancer cases from the registry database of the Japanese Organization of Hereditary Breast and Ovarian Cancer.

Results: 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.

Conclusions: 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.