Hemophagocytic lymphohistiocytosis associated with immune checkpoint inhibitor use: A review of the current knowledge and future directions

Hemophagocytic lymphohistiocytosis (HLH) is a severe and often lethal inflammatory syndrome characterized by excessive immune activation leading to fever, cytopenias, and multiorgan involvement. Immune checkpoint inhibitors (ICIs) are central to many contemporary cancer regimens, but their use is associated with immune-related adverse events. Here, we report a case of ICI-induced HLH successfully treated with single agent dexamethasone and provide a scoping review of the literature for cases of ICI-induced HLH with a focus on treatment strategies and outcomes. Using the Medline database, we searched for cases of ICI-associated HLH, with a total of 51 cases reported between 2017 and 2023. Our results underscore the severe nature of this disease, with a 13.7 % mortality rate across 51 case reports. Treatment strategies for ICI-induced HLH were variable: steroids alone (56.9 %), steroids with etoposide (17.6 %), steroids with tociluzumab (11.8 %), among other combinations. Our literature review indicates that steroids alone may be sufficient treatment in some cases of ICI-HLH, with comparable mortality with steroids alone (n = 29) (13.8 %) to that of cases treated with both steroids and immunomodulators (n = 15, 13.3 %). Moreover, all patients treated with steroids and tocilizumab survived (n = 6), suggesting that tocilizumab may be a reasonable next line of therapy when steroid monotherapy proves inadequate. We propose an outline for investigation and treatment of this rare complication of ICI use. Finally, we discuss possible future approaches to develop evidence-based strategies for the diagnosis and management of ICI-induced HLH including the importance of integrating the role of patient community involvement.