Successful Steroid Treatment of Pembrolizumab-induced Agranulocytosis That Developed after Splenectomy in a Patient with Non-small-cell Lung Cancer

Neutropenia, a rare immune-related adverse event, affects patients receiving treatment with immune check-point inhibitors (ICIs). We herein report a case of pembrolizumab-induced agranulocytosis. An 83-year-old man was diagnosed with advanced-stage lung carcinoma concomitant with splenomegaly complicated by hy-persplenism, causing pancytopenia. To avoid the risk of bone marrow suppression due to cytotoxic chemo-therapy, pembrolizumab monotherapy was chosen. However, the patient developed agranulocytosis despite the resolution of pancytopenia through splenectomy performed after the fourth pembrolizumab cycle. Neutrophil counts improved after steroid treatment but not after granulocyte colony-stimulating factor treatment. This case demonstrated that neutropenia can sometimes develop abruptly after several ICI therapy cycles.