Cardiovascular Toxicity of Novel HER2-Targeted Agents and Multikinase Inhibitors in Oncology: From Mechanisms to Real-World Clinical Evidence

The advent of novel Human Epidermal growth factor Receptor 2 (HER2)-targeted therapies and tyrosine kinase inhibitors (TKIs) has significantly improved outcomes in HER2-positive malignancies, particularly breast cancer. However, these agents carry a growing burden of cardiovascular adverse events, representing a critical concern in modern oncology. This narrative review explores the evolving landscape of cardiovascular toxicity associated with these therapeutic classes, integrating mechanistic insights with real-world clinical data. HER2-targeting monoclonal antibodies and antibody–drug conjugates exert off-target effects on cardiomyocytes via HER2 pathway inhibition, leading to reversible or irreversible myocardial dysfunction. In parallel, small-molecule TKIs, especially those targeting multiple kinases, have been associated with hypertension, arrhythmia, QT prolongation, and heart failure, through mechanisms such as mitochondrial dysfunction, endothelial damage, and disruption of cardioprotective signaling. We summarize clinical evidence elucidating the molecular basis of these toxicities and critically review clinical trials and post-marketing data highlighting their incidence and management. The review emphasizes the heterogeneity of cardiotoxicity profiles across different agents, underscoring the need for individualized cardiovascular risk stratification and monitoring. Finally, we address the emerging role of cardio-oncology in bridging oncologic efficacy with cardiac safety, advocating for multidisciplinary approaches, biomarker-guided surveillance, and standardized definitions of cardiotoxicity. As precision oncology advances, a parallel refinement in cardiotoxicity prediction and prevention is imperative to optimize patient outcomes.