IMPORTANCE: Clonal hematopoiesis of indeterminate potential (CHIP) is linked to an increased incidence of cardiovascular and malignant diseases. OBJECTIVE: To determine whether CHIP is associated with cardiotoxic effects in patients with breast cancer receiving trastuzumab. DESIGN, SETTING, AND PARTICIPANTS: Analyses of human cohorts with complementary animal experimentation were performed using a nationwide population-based cohort (UK Biobank), 1 tertiary referral center (Seoul National Univers...