Three-Year Outcomes Following Permissive Cardiotoxicity in Patients on Trastuzumab.

INTRODUCTION: Cardiotoxicity, manifest by reduced left ventricular ejection fraction (LVEF), is the most common reason for the premature discontinuation of trastuzumab. While permissive cardiotoxicity (where mild cardiotoxicity is accepted to enable ongoing trastuzumab) has been shown feasible, the longer-term outcomes are unknown. We aimed to study the intermediate-term clinical outcomes of patients who underwent permissive cardiotoxicity. MATERIALS AND METHODS: We performed a retrospective cohort study of patients referred to the cardio-oncology service at McMaster University from 2016 to 2021 for LV dysfunction following trastuzumab administration. RESULTS: Fifty-one patients underwent permissive cardiotoxicity. The median (25th-75th percentile) follow-up time from cardiotoxicity onset was 3 years (1.3-4 years). Forty-seven (92%) patients completed trastuzumab; 3 (6%) developed severe LV dysfunction or clinical heart failure (HF) while on trastuzumab and prematurely discontinued therapy. One discontinued trastuzumab by patient choice. At final follow-up after therapy completion, 7 (14%) patients still had mild cardiotoxicity, including 2 who had clinical heart failure and stopped trastuzumab early. Among those with recovered LV function, 50% had normalized LVEF or GLS by 6 and 3 months, respectively, after initial cardiotoxicity. There was no difference in characteristics between those who did or did not recover their LV function. CONCLUSIONS: Among patients exposed to permissive trastuzumab cardiotoxicity for HER2-positive breast cancer, 6% were unable to complete planned trastuzumab due to severe LV dysfunction or clinical HF. Although most patients recover their LV function after trastuzumab discontinuation or completion, 14% still have persistent cardiotoxicity by 3-year follow-up.