Incident Myocardial Infarction, Heart Failure, and Oncologic Outcomes in Breast Cancer Survivors.

Background: Cardiovascular disease (CVD) is associated with higher rates of incident cancer. Data are scarce regarding the association of incident CVD with oncologic outcomes after a cancer diagnosis. Objectives: This study sought to determine whether incident myocardial infarction (MI) or heart failure (HF) in breast cancer survivors is associated with oncologic outcomes. Methods: This was a population-based cohort study in Ontario, Canada, using linked administrative data sets of women diagnosed with first breast cancer between April 1, 2007, and March 31, 2015. A landmark analysis was conducted of women alive 2 years after breast cancer diagnosis, aged ≥40 years, and with available staging data and without recurrent/distant disease or preceding CVD. The exposure was a composite of MI and/or HF after the landmark date. The outcomes were cancer mortality, new non-breast malignancy diagnosis, and new chemotherapy initiation. Multivariable cause-specific hazards regression was used to determine the association of incident MI/HF (time-varying exposure) with outcomes. Results: A total of 30,694 women (median age of 60 years) were included, of whom 1,346 developed incident MI/HF at a median of 3.9 years after the landmark date. At 5 years, the cumulative incidence was 5.9% (95% CI: 5.6%-6.1%) for cancer death, 4.3% (95% CI: 4.1%-4.6%) for non-breast malignancy, and 25.7% (95% CI: 25.2%-26.2%) for new chemotherapy. Incident MI/HF was associated with a higher hazard of cancer death (HR: 3.94; 95% CI: 3.38-4.59), non-breast malignancy (HR: 1.39; 95% CI: 1.06-1.82), and new chemotherapy (HR: 1.25; 95% CI: 1.02-1.53). Conclusions: Incident MI and/or HF after breast cancer treatment are associated with higher hazards of adverse oncologic outcomes, highlighting the need to prioritize care for these patients.