Beyond Tumor Immunity: The Disruption of Endocrine and Infectious Homeostasis by Immune Checkpoint Inhibitors

Immune checkpoint inhibitors (ICIs) have revolutionized cancer treatment by reactivating T cell-mediated anti-tumor immunity. However, this enhanced immune activity can lead to immune-related adverse events (irAEs). This narrative review focuses on endocrine irAEs, including thyroid dysfunction, hypophysitis, adrenal insufficiency, and diabetes mellitus. It also explores infectious complications and their underlying mechanisms. These mechanisms include immune dysregulation resulting directly from ICI-induced T-cell activation and indirectly from the immunosuppressive therapies used to treat irAEs. Furthermore, potential role of endocrine irAEs in predisposing patients to infectious complications is analyzed. The objective is to provide non-oncology specialists with the clinical insight necessary to recognize and manage these complex side effects. This narrative review synthesizes current literature on the diagnosis, management, and pathophysiology of endocrine irAEs and infections associated with different classes of ICIs (anti-CTLA-4, anti-PD-1, and anti-PD-L1). Endocrine irAEs are common, with incidence varying by ICI type; combination therapies pose the highest risk. Thyroid dysfunction is the most frequent, followed by hypophysitis, which often leads to permanent secondary adrenal insufficiency. ICI-induced diabetes mellitus is a rare but serious complication, frequently presenting as diabetic ketoacidosis. ICIs are believed to induce a distinct array of infections resulting from immunological dysregulation, unrelated to immunosuppressive medication. The phenomenon is increasingly called ICI therapy-induced dysregulated immunity. Moreover, evidence suggests that endocrine irAEs can compromise immune function and lead to a significantly higher risk of bacterial and fungal infections. Identifying infections that imitate irAEs is particularly important because the therapy is significantly distinct. Greater interdisciplinary awareness is crucial for the early recognition and appropriate management of both the endocrine and infectious complications, ultimately improving the safety and outcomes for patients receiving immunotherapy.