Endocrine Abstracts

Immune checkpoint inhibitors (ICIs) are now integral to modern oncology treatments but could be associated with a spectrum of immune-mediated endocrine toxicities. Isolated ACTH deficiency is a recognised yet infrequent complication of PD-L1 inhibitors such as atezolizumab and may emerge following completion of treatment, highlighting the need for ongoing endocrine surveillance. Primary hypothyroidism is another ICI-related toxicity and may occur independently or alongside pituitary dysfunction. A 67-year-old man with advanced squamous cell carcinoma of the lung received atezolizumab between July 2020-July 2022. Four months after completing treatment, he presented with profound fatigue. Biochemical evaluation demonstrated secondary cortisol deficiency, with cortisol 59 nmol/l (normal 140–690) and ACTH 15 ng/l (normal 10–50). Thyroid tests revealed primary hypothyroidism: TSH 32.3 mU/l (normal 0.4–4.0) and free T4 6.5 pmol/l (normal 10–22). Anti-TPO and adrenal cortex antibodies were negative. Gonadal testing showed FSH 1.7 IU/l (normal 1.5–12), LH 1.5 IU/l (normal 1.8–9) and testosterone 7.8 nmol/l (normal 8–30), with normal prolactin and IGF-1. He failed his Short Synacthen Test with a low ACTH level, confirming secondary hypocortisolism. Pituitary MRI showed no structural abnormality, and CT imaging confirmed normal adrenal glands. Hydrocortisone and levothyroxine were commenced, with marked symptomatic improvement. After hormone optimisation, FSH, LH and testosterone normalised. His clinical condition stabilised with ongoing endocrine follow-up. Repeated Short Synacthen Tests and thyroid function tests up to three years after the initial diagnosis showed no recovery of either axis. This case illustrates that dual endocrine toxicity could be associated with PD-L1 inhibition, presenting as isolated ACTH deficiency consistent with immune-related hypophysitis together with concomitant primary hypothyroidism. These findings highlight the importance of long-term endocrine monitoring during and after ICI therapy to support timely diagnosis, appropriate hormone replacement and prevention of serious complications.