Abstract
<title>Abstract</title> <p> <bold>Background:</bold> Endocrine immune-related adverse events (irAEs) secondary to immune checkpoint inhibitors (ICIs) are documented in clinical research. Nevertheless, grade 3 immune-related hypophysitis attributable to the PD-L1 inhibitor adebrelimab has not been described in published literature, with merely mild grade 1-2 pituitary adverse reactions recorded during registration trials. This rare severe clinical case enriches the safety characteristics of adebrelimab and provides a reference basis for the clinical recognition and standardized management of pituitary irAEs. <bold>Case Presentation:</bold> A 60-year-old male patient diagnosed with extensive-stage small cell lung cancer (ES-SCLC) received combined chemotherapy plus adebrelimab induction therapy, followed by maintenance monotherapy with adebrelimab. After the 10th cycle of adebrelimab infusion, he developed persistent headache, orthostatic dizziness, severe fatigue and impaired self-care, unable to complete daily activities alone.Laboratory tests showed significantly reduced 8:00 a.m. and 4:00 p.m. adrenocorticotropic hormone (ACTH) and serum cortisol, decreased testosterone, while thyroid-stimulating hormone (TSH) and free thyroxine (FT4) remained within normal limits; Thyroid Peroxidase Antibody (TPOAb) tested positive. Cerebrospinal fluid examination revealed mild elevation of glucose and protein with scattered lymphocytes, and pituitary MRI showed no pituitary enlargement or abnormal contrast enhancement, and paraneoplastic antibodies were all negative. The grade 3 immune-related hypophysitis was confirmed, adebrelimab was permanently discontinued, and high-dose methylprednisolone was administered followed by gradual tapering. After standardized glucocorticoid intervention, the patient’s headache and fatigue were markedly relieved, and partial recovery of multiple pituitary axis functions was observed during follow-up. <bold>Conclusion:</bold> Long-term maintenance therapy with adebrelimab monotherapy may induce delayed grade 3 multi-axis immune-related hypophysitis, whose non-specific manifestations are easily confused with tumor progression or chemotherapy toxicities. Regular screening of full pituitary axis hormones is mandatory throughout ICI treatment. For patients presenting with unexplained fatigue, headache or orthostatic discomfort after adebrelimab administration, timely pituitary imaging and endocrine assessment should be arranged, and early glucocorticoid intervention can significantly improve clinical prognosis. </p>