A Case of Cytokine Release Syndrome (CRS) Related to Treatment With Lenvatinib Plus Pembrolizumab for Metastatic Clear Cell Renal Cell Carcinoma

Introduction Cytokine release syndrome (CRS) is a systemic inflammatory response triggered by various factors, including infection and immunotherapy. Due to its nonspecific presentation, distinguishing CRS from other life‐threatening conditions remains challenging. Case Presentation A 79‐year‐old male receiving lenvatinib plus pembrolizumab for metastatic renal cell carcinoma presented with high‐grade fever, altered mental status, and respiratory failure on day 4 of treatment. After excluding infectious etiologies and endocrine dysfunction, CRS was suspected and confirmed by elevated interleukin‐6 levels. Lenvatinib and pembrolizumab were discontinued, and the patient was treated with tocilizumab and dexamethasone. Clinical improvement was achieved by day 7. Conclusion CRS should be considered a potential cause of unexplained shock in patients receiving immune checkpoint inhibitors. Early diagnostic consideration is vital for timely intervention.