Abstract
BACKGROUND: Hemophagocytic lymphohistiocytosis (HLH) is a life-threatening hyperinflammatory syndrome characterized by supramaximal immune activation. Although rare, HLH has been increasingly recognized as an immune-related adverse event in patients undergoing immune checkpoint inhibitor (ICI) therapy. CASE PRESENTATION: We report the case of a female patient treated with concomitant radio-chemo-immunotherapy for cervical cancer (according to the KEYNOTE-A18 trial). She developed HLH following a single dose of pembrolizumab, presenting initially with immune-mediated pneumonitis and subsequently with fever, prolonged pancytopenia, and elevated inflammatory markers. After intensive diagnostics, broad-spectrum anti-infective treatment and granulocyte colony-stimulating factor (G-CSF) stimulation was started, without improvement. The diagnosis was finally made by HLH-2004 criteria, strongly indicated by an H‑score of 251 (> 99% probability of HLH). The HLH was successfully treated with corticosteroids alone. CONCLUSION: This case highlights the importance of early recognition and aggressive management of HLH secondary to immunotherapy, particularly in patients presenting with unexplained fever, G‑CSF-refractory cytopenia, and hyperferritinemia.