Introduction: Patients with human epidermal growth factor receptor 2 (HER2)-positive metastatic breast cancer (MBC) typically receive long-term trastuzumab treatment for several years. The aim of our study is to identify the incidence and characterize late-onset cardiotoxicity in patients with HER2-positive MBC receiving trastuzumab-based therapy.
Methods: We retrospectively reviewed charts of HER2-positive MBC patients who received >1 year of trastuzumab-based therapy at the Massachusetts General Hospital Cancer Center over three-year period. The primary endpoint was development of trastuzumab-induced cardiotoxicity (TIC). Secondary endpoints included time to TIC development, incidence/duration of trastuzumab interruption due to TIC, incidence of permanent discontinuation of trastuzumab due to TIC, clinic visit, or hospitalization due to TIC.
Results: Thirty-seven patients were included. Mean age was 56 years (range: 33-78 years, SD 9.5). Seven patients received prior doxorubicin and 14 patients received previous or concurrent breast irradiation. Mean duration of trastuzumab-based therapy was 57 months (range: 14-140 months, SD 39.3). Seven patients (18.9%) experienced TIC resulting in treatment interruption for two patients (28 and 78 days). The median time from starting trastuzumab therapy to TIC was 14 months (interquartile range: 11-29.5 months). The mean number of left ventricular ejection fraction (LVEF) assessment completed per year was 2.7 (range: 1.2-6.6, SD 1.1).
Conclusion: Cardiotoxicity occurred in a minority of patients with HER2-positive MBC receiving trastuzumab-based therapy for more than one year. LVEF reductions to below the institutional lower limit of normal and therapy modifications were uncommon.
Keywords: HER2-targeted therapy; cardiotoxicity; metastatic breast cancer; trastuzumab.