Immune checkpoint inhibitor-induced thyroid dysfunction in patients with pre-existing hypothyroidism: a case series

Kefah Bashir; Imane Boughaz; Daniel Morganstein; Kirsty Anderson; Paolo D

doi:10.1530/endoabs.117.P236

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Endocrine Abstracts (2026) 117 P236 | DOI: 10.1530/endoabs.117.P236

SFEBES2026 Poster Presentations Thyroid (34 abstracts)

Immune checkpoint inhibitor-induced thyroid dysfunction in patients with pre-existing hypothyroidism: a case series

Kefah Bashir ¹ , Imane Boughaz ¹ , Daniel Morganstein ¹ , Kirsty Anderson ² & Paolo D’Arienzo ²

Author affiliations

¹Chelsea and Westminster Hospital, London, United Kingdom; ²The Royal Marsden Hospital, London, United Kingdom

Background: Immune checkpoint inhibitors (ICIs) significantly improve survival across malignancies but often induce endocrine immune-related adverse events (irAEs). Thyroiditis is the most common endocrine irAE, typically presenting as transient thyrotoxicosis followed by hypothyroidism. However, data in patients with pre-existing hypothyroidism are limited.

Methods: We conducted a retrospective review of six patients with primary hypothyroidism who developed thyroid dysfunction during ICI therapy at a UK tertiary cancer centre. Thyroid function tests (TFTs), levothyroxine (LT4) dosing, symptoms, and outcomes were analysed.

Results: All six patients (aged 42–65) had thyroid dysfunction during ICI therapy (pembrolizumab, nivolumab, ipilimumab, or avelumab). • Four developed overt thyrotoxicosis (free T4: 25.3–39.7 pmol/l, TSH <0.02 mU/l); one had subclinical thyrotoxicosis, and one developed new-onset hypothyroidism (TSH 35.9 mU/l, T4 3.5 pmol/l). • Symptoms included palpitations (n = 3), fatigue (n = 4), and atrial fibrillation (n = 1). • LT4 was initially withheld in 2, increased in 2 (up to 150 µg/day), and reduced or adjusted in the remainder. Notably, 4/6 patients required higher LT4 doses post-ICI, suggesting increased irreversible thyroid damage. Two patients remain stable on LT4; four died due to cancer progression.

Conclusion: ICI-induced thyroiditis can occur in patients with pre-existing hypothyroidism and often follows a biphasic pattern, complicating LT4 titration. Higher LT4 needs post-treatment suggest more severe thyroidal destruction than typical autoimmune hypothyroidism. Close biochemical monitoring and multidisciplinary management are essential for optimal outcomes.

References: 1. Robert C. Nat Commun. 2020;11:3801. 2. Muir CA et al. J Clin Endocrinol Metab. 2020;105(11):dgaa517. 3. Chaker L et al. Lancet. 2022;400:791–806. 4. Mosaferi T et al. J Clin Endocrinol Metab. 2022;107(8):e3284–e3292.

Keywords: immune-related adverse events, thyroiditis, hypothyroidism, immunotherapy, levothyroxine