Beyond the Tumour: An Endocrine Pitfall of Immunotherapy

Immune checkpoint inhibitors (ICIs) such as pembrolizumab have transformed the treatment of advanced melanoma but are associated with immune-related adverse events (irAEs), including endocrine dysfunction such as adrenal insufficiency, which may be permanent and life-threatening. We report the case of a 62-year-old woman with Stage III BRAF-negative cutaneous melanoma of the left upper arm who developed pembrolizumab-induced adrenal insufficiency after three cycles of adjuvant therapy. She presented with gastrointestinal symptoms and systemic inflammation, and subsequent evaluation revealed cortisol <25 nmol/L with undetectable adrenocorticotropic hormone, consistent with secondary adrenal insufficiency. Pembrolizumab was discontinued, and she remains clinically stable on hydrocortisone replacement with surveillance imaging showing no evidence of recurrence. This case underscores the importance of vigilance for irAEs in patients receiving ICIs, as adrenal insufficiency can present with nonspecific symptoms and may be misdiagnosed without timely biochemical evaluation. Regular monitoring and early endocrine involvement are essential for accurate diagnosis and effective long-term management.