ERBB2 and heart failure: Patients with HER2+ eBC face additional cardiotoxicity risks from anti-HER2 drugs, including heart failure (2.5–4%) and decline in left ventricular ejection fraction (LVEF) (3–27%), meaning that cardiac monitoring is required before, during (every 3 months), and after (every 6 months for 2 years) treatment [88,89].