Incident cardiovascular events in women with left-sided versus right-sided breast cancer: a propensity score-matched study.

Background: The cardiotoxic effects of breast cancer (BC) therapies, including drugs and radiotherapy (RT), may increase cardiovascular morbidity, particularly atrial fibrillation (AF). The specific impact of BC laterality on the incidence of cardiovascular events remains unclear. To evaluate laterality-specific cardiovascular risks in women with left-sided versus right-sided BC using a large international cohort.

Methods: This cohort study used global healthcare data from the TriNetX network. Propensity score matching (1:1) was used to select a cohort of women with left-sided or right-sided BC, and follow-up was conducted with a maximum duration of 8 years. Mortality, AF, ventricular tachyarrhythmia, heart failure and implantation of an ICD during follow-up. HRs, cumulative incidences and 95% CIs were calculated for evaluating the treatment effect among the treated patients.

Results: During follow-up (median 3.2 years), left-sided BC (compared with right-sided BC) was associated with a similar risk of all-cause death and of all incident cardiovascular events with the notable exception of a significantly higher risk of AF (HR 1.051, 95% CI 1.016 to 1.088, p=0.004). There was no statistical interaction for this higher risk of AF associated with left-sided BC when considering women treated with RT (1.024 (95% CI 0.941 to 1.113), p=0.58) or no RT (HR 1.045 (95% CI 1.006 to 1.084), p=0.02, p for interaction 0.66) CONCLUSIONS: In this large international analysis, left-sided BC was significantly associated with a numerically marginal but statistically significant higher risk of AF than right-sided BC, while there were no differences for BC laterality regarding all-cause death and other cardiovascular events.