Cardiotoxicity after Additional Administration of Pertuzumab following Long-Term Trastuzumab: Report of 2 Cases.

Pertuzumab, a humanized antibody drug, has improved outcomes of patients with human epidermal growth factor receptor 2 (HER2)-positive breast cancer, when administered in combination with trastuzumab and other chemotherapies. Cardiotoxicity due to trastuzumab is widely recognized, while data on pertuzumab-based treatments in daily clinical practice are lacking. We herein report 2 Japanese patients, aged 72 and 49 years, who developed left ventricular dysfunction after pertuzumab administration, following long-term trastuzumab treatments. Both patients underwent curative surgery for their HER2-positive breast cancer and received anthracycline-based treatments. After developing metastatic disease, trastuzumab-based treatments were administered without cardiac toxicity, but both patients developed left ventricular dysfunction after pertuzumab administration (6 and 13 cycles, respectively). Although several large randomized trials have shown no additive effect of pertuzumab on cardiac dysfunction, careful monitoring of cardiac function appears to be necessary in daily practice, particularly for patients with prior long-term trastuzumab treatments.