Cytokine Release Syndrome Induced by Neoadjuvant Pembrolizumab in Early Triple-Negative Breast Cancer: A Case Report with Implications for Early Diagnosis and Management.

Introduction: Cytokine release syndrome (CRS) is a rare but potentially severe immune-related adverse event associated with immune checkpoint inhibitor (ICI) therapy. CRS is characterized by high fever, hemodynamic instability, and potential multi-organ dysfunction. Pembrolizumab, an ICI, is increasingly used as a standard perioperative treatment for triple-negative breast cancer (TNBC). However, reports of CRS in TNBC remain scarce. Case Presentation: We report the case of a 63-year-old woman diagnosed with TNBC (T3N2M0, Stage IIIA) who received pembrolizumab plus chemotherapy. On day 1 of the third cycle, she developed a high fever and headache within hours of pembrolizumab administration. On day 2, hypotension, tachypnea, hypoxia, and hepatic and renal dysfunction were observed. Suspecting CRS, the patient was admitted to the intensive care unit (ICU) and treated with tocilizumab and steroid pulse therapy, resulting in rapid clinical improvement. On day 4, the patient was discharged from the ICU. She was started on oral prednisolone with gradual tapering; however, she experienced CRS recurrence. The patient underwent surgery rather than resuming chemotherapy. At 20 months postoperatively, neither breast cancer relapse nor CRS recurrence was observed. Conclusion: Early diagnosis and treatment of CRS are crucial to prevent severe multi-organ failure.