The Temporal Risk of Heart Failure Associated With Adjuvant Trastuzumab in Breast Cancer Patients: A Population Study

Background: The late cardiac effect of adjuvant trastuzumab and its potential interaction with anthracycline have not been well-studied on a population level. Methods: In this retrospective population-based cohort study, female breast cancer patients in Ontario, diagnosed between 2003 and 2009, were identified by the Ontario Cancer Registry and linked to administrative databases to ascertain demographics, cardiac risk factors, comorbidities, and use of adjuvant trastuzumab and other chemotherapy. Patients with pre-existing heart failure (HF) were excluded. The main endpoint was new diagnosis of HF. Analyses included Kaplan-Meier (KM) survival analysis, multivariable piecewise Cox regression, and competing risk and propensity score analyses. All statistical tests were two-sided. Results: Nineteen thousand seventy-four women with breast cancer treated with adjuvant chemotherapy were identified, of whom 3371 (17.7%) also received adjuvant trastuzumab. Anthracycline use was 84.9% overall. After a median follow-up of 5.9 years, patients treated with trastuzumab and chemotherapy were more likely to develop HF than patients on chemotherapy alone (5-year cumulative incidences of 5.2% vs 2.5%; log-rank P < .001). After adjusting for confounders, adjuvant trastuzumab remained independently associated with incident HF in the first 1.5 years (HR = 5.77, 95% CI = 4.38 to 7.62, P < .001), but not thereafter (HR = 0.87, 95% CI = 0.57 to 1.33, P = .53). Anthracycline use did not increase the risk of HF with trastuzumab synergistically, neither within (P-interaction = .92) nor beyond 1.5 years (P-interaction = .23). Conclusion: Adjuvant trastuzumab was associated with increased risk of new incidence of HF in breast cancer survivors during the period of adjuvant treatment but not thereafter. Routine intensive monitoring may not be necessary after completing adjuvant therapy.