Endocrine Abstracts

Background: Immune checkpoint inhibitors (ICIs), such as pembrolizumab, are increasingly used to treat advanced malignancies, including renal cell carcinoma. Thyroid dysfunction is a well-recognised immune-related adverse event (irAE) of ICIs, commonly presenting as transient thyrotoxicosis followed by hypothyroidism.¹ This case report highlights overt hypothyroidism developing in a patient with previously normal thyroid function following pembrolizumab therapy.

Case Presentation: A 70-year-old man with multiple comorbidities—ischemic heart disease, heart failure with reduced ejection fraction, chronic obstructive pulmonary disease, hypertension, atrial fibrillation, psoriasis, and a history of prostate cancer treated via robotic prostatectomy—was admitted with chest sepsis requiring inotropic support. Incidentally, CT imaging revealed two renal masses with heterogeneous enhancement, regional lymphadenopathy, and a suspected tumour thrombus extending into the renal vein and inferior vena cava. He underwent robotic right nephrectomy with excision of the tumour thrombus. Postoperatively, pembrolizumab therapy was initiated. Baseline thyroid function tests were normal (TSH 0.45mIU/l). Within weeks, he developed overt hypothyroidism, evidenced by a markedly elevated TSH of 49.60 mIU/l and a low free T4 (<3.2 pmol/l). Levothyroxine treatment was started, and the patient is under close follow-up with regular thyroid function tests and outpatient thyroid ultrasound.

Conclusion: Pembrolizumab-induced thyroid dysfunction is a frequent irAE, with hypothyroidism occurring in up to 10% of patients.² The pathophysiology may involve destructive thyroiditis or autoimmune mechanisms, even in patients without prior thyroid disease.This case underscores the importance of routine thyroid function monitoring during ICI therapy. Early recognition and management of endocrine irAEs are essential to safely continue immunotherapy and optimise patient outcomes.³

References: 1. Iwama et al. reviewed endocrinology advances in clinical metabolism (Best Pract Res Clin Endocrinol Metab, 2022). 2. Pollack et al. studied cancer immunology and therapy responses (Cancer Immunol Res, 2018). 3. Barroso-Sousa et al. examined immune-related adverse events in cancer (JAMA Oncol, 2018).