ABSTRACT
PURPOSE: Breast cancer (BC) is the most common secondary cancer and has poorer survival than primary BC (pBC) after any prior malignancy. For BC survivors, developing a contralateral secondary BC (CSBC) is the most frequent second-cancer event and is currently treated similarly to pBC. Identifying survival differences between pBC and CSBC could influence future counseling and treatments for patients with CSBC. METHODS: Women (≥15 years) diagnosed with pBC from 1991 to 2015 in the California Cancer Registry (n = 377,176) were compared with those with CSBC (n = 15,586) by age group (15-39 years, n = 406; 40-64 years, n = 6814; ≥ 65 years, n = 8366). Multivariable logistic regression models assessed factors associated with CSBC. Multivariable Cox proportional hazards regression models assessed BC-specific survival (BCSS), while accounting for the competing risk of death. RESULTS: Across all ages, CSBC patients were more likely to have smaller tumors (T2 vs. T1a; 15-39 yeras: OR 0.25, CI 0.16-0.38; 40-64 years: OR 0.41, CI 0.37-0.45; ≥ 65 years: OR 0.46, CI 0.42-0.51) and lymph node-negative disease (positive vs. negative; 15-39 years: OR 0.86, CI 0.69-1.08; 40-64 years: OR 0.88, CI 0.83-0.93; ≥ 65 years: OR 0.89, CI 0.84-0.94). Additionally, CSBC was associated with worse survival compared with pBC across all ages (15-39 years: HR 2.73, CI 2.30-3.25; 40-64 years: HR 2.13, CI 2.01-2.26; ≥ 65 years: HR 1.52, CI 1.43-1.61). CONCLUSION: BCSS is worse among all women diagnosed with CSBC compared with pBC, with the strongest impact seen in adolescent and young adult women. Worse survival after CSBC, despite associations with smaller tumors and lymph node negativity, suggests that CSBC may need eventual treatment reconsideration.
