Cytokine Release Syndrome More than Two Years after Pembrolizumab Introduction.

A 71-year-old man with advanced lung adenocarcinoma was treated with carboplatin, pemetrexed, and pembrolizumab in June 2020. Pemetrexed and pembrolizumab maintenance therapy were continued until November 2022. A fever and severe fatigue occurred in December 2022; however, the cause of the infection was inconclusive based on the patient's symptoms, imaging findings, and culture tests. Although the patient was administered antibiotics, his general condition worsened. Considering the possible diagnosis of immune-related cytokine release syndrome (CRS), the patient was administered prednisolone (1 mg/kg/day) and showed improvement. In conclusion, CRS can occur even long after the initial administration of immune checkpoint inhibitor therapy.