Abstract #1402123: A Rare Case of Hypophysitis with Isolated ACTH Deficiency and Thyroiditis Complicating Treatment with Pembrolizumab

Immune checkpoint inhibitors (CPIs) have been shown to be beneficial in the treatment of cancers by enhancing antitumor immunity. CPIs block intrinsic down regulators immunity, such as cytotoxic T lymphocyte antigen 4 (CTLA-4) and programmed cell death 1 (PD-1) or its ligand (PD-L1). While useful for targeting malignant tissue, can destructive effects on normal tissues, including endocrine organs. Hypophysitis is more common those receiving anti-CTLA-4 therapy (up 10% patients) than anti-PD1-therapy (<1% whereas opposite stands true thyroiditis. We present a rare case woman with breast cancer treated anti-PD-1 pembrolizumab who developed isolated ACTH deficiency from hypophysitis along A 39-year-old female presented several weeks fatigue confusion. On exam, she was well-appearing normotensive. Cortisol TSH were found low at <0.1ug/dL <0.01uIU/mol, respectively, raising concern central adrenal insufficiency hypothyroidism. Free T4 free T3 high indicating primary thyroid rather pituitary dysfunction. Cosyntropin stimulation test showed an insufficient rise cortisol 1.7ug/dL, which, inappropriately 9.9pg/mL, confirmed diagnosis insufficiency. Sellar MRI revealed no abnormalities. Adrenal hydrocortisone. Hyperthyroidism quickly transitioned hypothyroidism, supporting thyroiditis, which levothyroxine. Pembrolizumab stopped later resumed once clinical symptoms stabilized while hormonal therapy. associated variety immune mediated adverse events, hypophysitis, dysfunction, autoimmune diabetes, adrenalitis. Although thyroiditis most commonly reported event therapy, other events occur, rarely. supported sellar changes MRI, it important clinicians aware that anti-PD1 may lack classic changes. As dysfunction life-threatening often overlap malignancy related treatments, index suspicion necessary ensure prompt treatment. In addition, screening recommended all patients CPIs.