Immune checkpoint inhibitor-induced radiation recall myositis

Dear Editor, Radiation recall (RR) is a rare acute inflammatory reaction that occurs at the irradiation site after the administration of certain chemotherapeutic agents, such as gemcitabine. Patients with RR generally present with dermatitis [1], pneumonia and esophagitis; however, only a few cases of RR with myositis [i.e. radiation recall myositis (RRM)] have been reported in the relevant literature [2, 3]. The reported mean duration from last radiation exposure to the onset of RRM is 5.3 ± 1.5 months [3]. In the present case, the onset of myositis was 4 months after the last radiotherapy, consistent with previous reports, imaging results and histopathological findings. Immune checkpoint inhibitors (ICIs), which are monoclonal antibodies engineered to target cytotoxic T lymphocyte antigen 4, programmed cell death protein 1 (PD-1) or programmed cell death-1 ligand 1 (PD-L1) (which help cytotoxic T cells to kill cancer cells), have been increasingly used in recent years. Moreover, ICIs have transformed the treatment landscape for many patients with advanced malignancies. However, there are concerns regarding immune-related adverse events associated with ICIs. We herein report a case of ICI-induced RRM.