Pembrolizumab-Induced Adrenal Insufficiency Presenting Eight Months After Cessation of Treatment

Pembrolizumab is a monoclonal antibody that functions as an immune checkpoint inhibitor. It is an FDA-approved immunotherapy used to treat various malignancies. With its wide use in cancer therapy, there are many known side effects. It is a common cause of endocrinopathies such as thyroid disease and adrenal insufficiency (AI). AI has been most commonly reported during active treatment cycles with pembrolizumab, as well as quickly after the termination of treatment. However, we describe a case of pembrolizumab-induced AI with an onset at eight months following the discontinuation of treatment and discuss prompt treatment when AI is diagnosed.