Risk of contralateral breast cancer according to first breast cancer characteristics among women in the USA, 1992-2016

Abstract

Background: Estimates of contralateral breast cancer (CBC) risk in the modern treatment era by year of diagnosis and characteristics of the first breast cancer are needed to assess the impact of recent advances in breast cancer treatment and inform clinical decision making.

Methods: We examined CBC risk among 419,818 women (age 30-84 years) who were diagnosed with a first unilateral invasive breast cancer and survived ≥ 1 year in the US Surveillance, Epidemiology, and End Results program cancer registries from 1992 to 2015 (follow-up through 2016). CBC was defined as a second invasive breast cancer in the contralateral breast ≥ 12 months after the first breast cancer. We estimated standardized incidence ratios (SIRs) of CBC by year of diagnosis, age at diagnosis, and tumor characteristics for the first breast cancer. Cumulative incidence of CBC was calculated for women diagnosed with a first breast cancer in the recent treatment era (2004-2015, follow-up through 2016).

Results: Over a median follow-up of 8 years (range 1-25 years), 12,986 breast cancer patients developed CBC. Overall, breast cancer patients had approximately twice the risk of developing cancer in the contralateral breast when compared to that expected in the general population (SIR = 2.21, 95% CI = 2.17-2.25). SIRs for CBC declined by year of first diagnosis, irrespective of age at diagnosis and estrogen receptor (ER) status (p-trends < 0.001), but the strongest decline was after an ER-positive tumor. The 5-year cumulative incidence of CBC ranged from 1.01% (95% CI = 0.90-1.14%) in younger women (age < 50 years) with a first ER-positive tumor to 1.89% (95% CI = 1.61-2.21%) in younger women with a first ER-negative tumor.

Conclusion: Declines in CBC risk are consistent with continued advances in breast cancer treatment. The updated estimates of cumulative incidence inform breast cancer patients and clinicians on the risk of CBC and may help guide treatment decisions.

Keywords: Breast cancer; Contralateral breast cancer; SEER.

Fig. 1

Criteria for defining contralateral breast cancer cases among women diagnosed with a first breast cancer between 1992 and 2015 and followed through 2016 in 12 SEER registries

Fig. 2

Temporal trends in SIRs for contralateral breast cancer overall and excluding women with contralateral prophylactic mastectomy (CPM) among 1-year survivors of a first primary breast cancer in 12 SEER registries, 1992–2016. Estimates for contralateral breast cancer by calendar period of first breast cancer diagnosis are a overall, and according to b age at first breast cancer diagnosis, c ER status of first breast cancer, d after ER-positive breast cancer by age at first diagnosis, and e after ER-negative breast cancer by age at first diagnosis. Gray dashed lines indicate exclusion of CPM