Risks of contralateral breast cancer in BRCA1 and BRCA2 mutation carriers

Mutations in BRCA1 and BRCA2 confer high lifetime risks of breast cancer. Previous studies have suggested, following an initial diagnosis, the risk for a contralateral breast cancer is approximately 3% annually or up to 40% at 10 years. The results presented here are of contralateral breast cancer risk in BRCA1/BRCA2 mutation carriers.

Three hundred and seventy-four BRCA1 mutation carriers and 346 BRCA2 mutation carriers were followed up for up to 30 years following breast cancer diagnosis. The incidence of a contralateral breast cancer and the effect of tamoxifen use and oophorectomy on this were observed.

Follow-up over a 25-year to 30-year period shows a constant 2% annual risk of contralateral breast cancer in BRCA1/BRCA2 mutation carriers. This risk is not affected by age at diagnosis of first breast cancer. Over the follow-up period, oophorectomy, if performed below the age of 45 years, led to a reduction in contralateral breast cancer risk of 40%. Tamoxifen use was shown to reduce the risk of a contralateral breast cancer in the first 6 years following initial diagnosis but no effect was seen after this period. Over the full follow-up period, tamoxifen use did not significantly reduce the risk.

Women who carry a BRCA1/BRCA2 mutation who have had breast cancer have a constant increased risk of a second contralateral breast tumour. Oophorectomy has a greater impact on reducing this risk than tamoxifen use.