Endocrine Abstracts

Background: Immune checkpoint inhibitors (ICIs) targeting PD-1, PD-L1 or CTLA-4 have transformed cancer therapy across multiple malignancies. However, they can induce immune-related adverse events (irAEs), with thyroid dysfunction being the most common endocrine toxicity. This audit assessed the incidence, timing and management of thyroid dysfunction in patients receiving ICIs, and evaluated projected implications for endocrine service provision.

Methods: A retrospective review was conducted of patients who received ICIs at St. James’s Hospital, Dublin, between July and December 2022. Data collected included cancer type, immunotherapy regimen, thyroid function test (TFT) abnormalities, dates of onset and resolution, and whether levothyroxine was initiated. Management was assessed against European Society of Endocrinology guidelines. Q4 2024 prescribing data was then used to more accurately estimate future impact, given the exponential growth of ICI use since 2022.

Results: Of 96 patients, 10.4% developed thyroiditis (median onset 31 days; resolution 35 days), 9.4% developed hypothyroidism without preceding thyroiditis (median onset 105 days), and 47.9% had other TFT derangements. Among 11 patients initiated on levothyroxine, 9 were treated in accordance with guideline recommendations. There was no significant association between cancer type and thyroid irAE (P = 0.138), but a trend toward significance with ICI type was noted (P = 0.07). Based on prescribing trends, approximately 412 patients may receive ICIs between July and December 2025, with an estimated 43 developing thyroiditis, 39 hypothyroidism, and 197 with TFT derangements requiring clinical interpretation.

Conclusions: Thyroid dysfunction is a frequent IRAE following ICIs, with early onset in most cases. These findings highlight the need for proactive TFT monitoring and structured endocrine-oncology collaboration to support the growing immunotherapy patient population.