The risk of contralateral breast cancer: a SEER-based analysis

BACKGROUND: We sought to estimate the annual risk and 25-year cumulative risk of contralateral breast cancer among women with stage 0-III unilateral breast cancer. METHODS: We identified 812,851 women with unilateral breast cancer diagnosed between 1990 and 2015 in the SEER database and followed them for contralateral breast cancer for up to 25 years. Women with a known bilateral mastectomy were excluded. We calculated the annual risk of contralateral breast cancer by age at diagnosis, by time since diagnosis and by current age. We compared risks by ductal carcinoma in situ (DCIS) versus invasive disease, by race and by oestrogen receptor (ER) status of the first cancer. RESULTS: There were 25,958 cases of contralateral invasive breast cancer diagnosed (3.2% of all patients). The annual risk of contralateral breast cancer over the 25-year follow-up period was 0.37% and the 25-year actuarial risk of contralateral invasive breast cancer was 9.9%. The annual risk varied to a small degree by age of diagnosis, by time elapsed since diagnosis and by current age. The 25-year actuarial risk was similar for DCIS and invasive breast cancer patients (10.1 versus 9.9%). The 25-year actuarial risk was higher for black women (12.7%) than for white women (9.7%) and was lower for women with ER-positive breast cancer (9.5%) than for women with ER-negative breast cancer (11.2%). CONCLUSIONS: Women with unilateral breast cancer experience an annual risk of contralateral breast cancer similar to 0.4% per year, which persists over the 25-year follow-up period.