Race, ethnicity and risk of second primary contralateral breast cancer in the United States

Abstract

Breast cancer survivors have a high risk of a second primary contralateral breast cancer (CBC), but there are few studies of CBC risk in racial/ethnic minority populations. We examined whether the incidence and risk factors for CBC differed by race/ethnicity in the United States. Women with a first invasive Stage I-IIB breast cancer diagnosis at ages 20-74 years between 2000 and 2015 in the Surveillance, Epidemiology, and End Results Program (SEER) 18 registries were followed through 2016 for a diagnosis of invasive CBC ≥1 year after the first breast cancer diagnosis. We used cause-specific Cox proportional hazards models to test the association between race/ethnicity and CBC, adjusting for age, hormone receptor status, radiation therapy, chemotherapy and stage at first diagnosis, and evaluated the impact of contralateral prophylactic mastectomy, socioeconomic status, and insurance status on the association. After a median follow-up of 5.9 years, 9247 women (2.0%) were diagnosed with CBC. Relative to non-Hispanic (NH) White women, CBC risk was increased in NH Black women (hazard ratio = 1.44, 95% CI 1.35-1.54) and Hispanic women (1.11, 95% CI 1.02-1.20), with the largest differences among women diagnosed at younger ages. Adjustment for contralateral prophylactic mastectomy, socioeconomic status and health insurance did not explain the associations. Therefore, non-Hispanic Black and Hispanic women have an increased risk of CBC that is not explained by clinical or socioeconomic factors collected in SEER. Large studies of diverse breast cancer survivors with detailed data on treatment delivery and adherence are needed to inform interventions to reduce this disparity.

Keywords: contralateral breast cancer; ethnicity; race; second primary cancer; survivorship.

Figure 1:

Abbreviations. CBC, contralateral breast cancer; API, Asian / Pacific Islander; AIAN, American Indian / Alaska Native Cumulative incidence of CBC among one-year survivors of a first primary invasive breast cancer. Cumulative incidence estimates account for competing risks of death and other second primary invasive cancer diagnoses. The P-value is a test for difference of the cumulative incidence of CBC across race/ethnicity groups.

Figure 2:

Abbreviations. CBC, contralateral breast cancer; NH, Non-Hispanic Age-specific incidence per 100,000 person-years of 2^nd primary breast cancer and first primary breast cancer in SEER 18 registries (2000 – 2016).

Figure 3:

Abbreviations. Hazard Ratio, HR; NH, Non-Hispanic; ER, Estrogen Receptor. HRs of CBC estimated for each race/ethnicity group in stratified multivariable Cox proportional hazards models relative to non-Hispanic White women and adjusting for ER status of the first breast cancer, PR status of the first breast cancer, radiation therapy for the first breast cancer, chemotherapy for the first breast cancer, stage of first breast cancer, with conditioning on year of diagnosis. (A) Multivariable models stratified by age at diagnosis of the first primary breast cancer. (B) Multivariable models stratified by ER status of the first primary breast cancer.