A large retrospective review reports that the checkpoint inhibitor nivolumab can trigger cytokine release syndrome (CRS), including severe and potentially deadly presentations. Published in Supportive Care in Cancer, the analysis compiles the largest case review to date of CRS tied to nivolumab, emphasizing the systemic inflammatory risk associated with immune activation. The findings arrive as oncology continues to deepen use of PD-1 pathway inhibitors across tumor types, where clinicians already monitor for immune-related adverse events. A CRS signal adds another layer to risk assessment, particularly for patients with rapidly progressing disease or those receiving combination regimens. For biotech teams developing immunotherapies and biosimilars, the work supports closer hemovigilance and earlier management pathways—especially because CRS may present with overlapping symptoms across different immune toxicity syndromes.