Contralateral breast cancer risk according to first breast cancer characteristics among United States women from 1992 to 2015.

Abstract

1549 Background: After recent advances in breast cancer treatment and increasing uptake of contralateral prophylactic mastectomies, estimates of contralateral breast cancer (CBC) risk by year of diagnosis and other patient characteristics are needed to help inform decision making. Methods: We estimated CBC risk in 399,032 1-year survivors of a first primary breast cancer (stage I-III) in the US Surveillance, Epidemiology, and End Results Database (1992-2015). CBC was defined as an invasive second breast cancer diagnosed in the opposite breast 12+ months after the first breast cancer diagnosis. We estimated standardized incidence ratios (SIRs) and 5-year cumulative incidence of CBC by calendar period, age, breast cancer subtype, and receipt of hormonal therapy for the initial breast cancer. SIRs were calculated as the observed number of CBCs among survivors compared to the expected number of first breast cancers in the general population. Cumulative incidence was estimated in women without contralateral prophylactic mastectomies and accounted for competing risks. Results: Among 399,032 breast cancer survivors, 11,365 cases of CBC were diagnosed through 2015. Risk of CBC was elevated over the entire study period (SIR = 2.23, 95% CI = 2.19-2.27). SIRs for CBC declined over calendar period and this decreasing trend was observed irrespective of age, estrogen receptor (ER) status, and hormonal therapy. Survivors had an overall 5-year cumulative incidence of CBC of 1.49% (95% CI = 1.44%-1.54%), which decreased over time to 1.31% (95% CI = 1.23%-1.41%) in 2008-2014. For recent diagnoses, the 5-year cumulative incidence of CBC was higher after ER-negative (1.80%, 95% CI = 1.55%-2.07%) and triple negative tumors (1.98%, 95% CI = 1.52%-2.55%), and lowest for women who received hormonal therapy (1.01%, 95% CI = 0.90%-1.13%). Conclusions: Although CBC risk is declining in the US from 1992-2015, survivors have approximately twice the risk of an incident breast cancer (in the contralateral breast) compared to the general population. The 5-year cumulative risk of CBC is highest after ER-negative/triple negative tumors highlighting the need for medical surveillance and targeted interventions among these patients.