Granulomatous myositis induced by anti–PD-1 monoclonal antibodies

With the expanding use of immune checkpoint blockers typified by anti–programmed death-1 (PD-1) and anti–cytotoxic T-lymphocyte-associated protein 4 monoclonal antibodies (Abs) for antitumor therapy, the number of patients showing immune-related adverse events (irAEs) is increasing. Skeletal muscle is one of the target tissues of irAEs and several features of myopathy as irAEs have been reported: myasthenia gravis (MG) overlap, cardiac involvement, necrotizing myopathy, and inflammatory myopathy with T-cell and B-cell infiltration.1–4 However, the immunopathogenesis of muscle destruction remains unclear. Here, we report 2 cases of granulomatous myositis after anti–PD-1 therapy. The authors thank Drs. Ryo Usui, Keiichi Hokkoku (Teikyo University School of Medicine), Tatsuhiko Naito, Masao Osaki, and Yoshikazu Uesaka (Toranomon Hospital) for help in the acquisition of clinical data of the patients.