Risks of subsequent primary cancers among breast cancer survivors according to hormone receptor status

Background: This study was aimed at examining the risks of subsequent primary cancers (SPCs) among breast cancer survivors by hormone receptor (HR) status and age at diagnosis. Methods: Data from 12 Surveillance, Epidemiology, and End Results registries were used to identify 431,222 breast cancer survivors (at least 1 year) diagnosed between the ages of 20 and 84 years from 1992 to 2015. Risks of SPCs were measured as the standardized incidence ratio (SIR) and the excess absolute risk (EAR) per 10,000 person-years. Poisson regression was used to test the difference in SIRs by HR status. Results: In comparison with the general population, the risk of new cancer diagnoses among survivors was 20% higher for those with HR-positive cancers (SIR, 1.20; 95% confidence interval [CI], 1.19-1.21; EAR, 23.3/10,000 person-years) and 44% higher for those with HR-negative cancers (SIR, 1.44; 95% CI, 1.41-1.47; EAR, 45.2/10,000 person-years), with the risk difference between HR statuses statistically significant. The higher risk after HR-negative cancer was driven by acute nonlymphocytic leukemia and breast, ovarian, peritoneal, and lung cancers. By age at diagnosis, the total EAR per 10,000 person-years ranged from 15.8 (95% CI, 14.1-17.5; SIR, 1.11) among late-onset (age, 50-84 years) HR-positive survivors to 69.4 (95% CI, 65.1-73.7; SIR, 2.24) among early-onset (age, 20-49 years) HR-negative survivors, with subsequent breast cancer representing 73% to 80% of the total EAR. After breast cancer, the greatest EARs were for ovarian cancer among early-onset HR-negative survivors, lung cancer among early- and late-onset HR-negative survivors, and uterine corpus cancer among late-onset HR-positive survivors. Conclusions: Risks of SPCs after breast cancer differ substantially by subtype and age. This suggests that more targeted approaches for cancer prevention and early-detection strategies are needed in survivorship care planning.