Pembrolizumab-Induced Smoldering Myocarditis in Patients With Triple-Negative Breast Cancer

Immune checkpoint inhibitors (ICI), in combination with chemotherapy, have been approved for the treatment of triple-negative breast cancer (TNBC). ICI-induced myocarditis is a rare complication with a high mortality rate. Diagnosis of ICI-induced myocarditis can be challenging because of the heterogeneity of clinical presentation, histopathological studies, and severity of disease. Smoldering myocarditis is a subclinical myocarditis in which patients are asymptomatic or present with mild, nonspecific signs and symptoms. To date, there have been no reports on the incidence, characteristics, or outcomes of ICI-induced SM in TNBC. Herein, we highlight 2 cases of pembrolizumab-induced smoldering myocarditis in patients treated with ICI for TNBC.