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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.