Background Thyroid dysfunction occurs commonly following immune checkpoint inhibition. The etiology of thyroid immune-related adverse events (irAEs) remains unclear and clinical presentation can be variable. This study sought to define thyroid irAEs following immune checkpoint inhibitor (ICI) treatment and describe their clinical and biochemical associations. Methods We performed a retrospective cohort study of thyroid dysfunction in patients with melanoma undergoing CTLA-4 and/or PD-1 based ICI treatment from Nov 1, 2009 to Dec 31, 2019. Thyroid function was measured at baseline and at regular intervals following the start of ICI-treatment. Clinical and biochemical features were evaluated for associations with ICI-associated thyroid irAEs. The prevalence of thyroid autoantibodies and the effect of thyroid irAEs on survival were analysed. Results A total of 1246 patients were included with a median follow-up of 11.3 months. 518 (42%) patients developed an ICI-associated thyroid irAE. Subclinical thyrotoxicosis (n=234) was the most common thyroid irAE, followed by overt thyrotoxicosis (n=154), subclinical hypothyroidism (n=61), and overt hypothyroidism (n=39). Onset of overt thyrotoxicosis occurred a median of 5 weeks (IQR 2-8) after receipt of first dose of ICI. Combination immunotherapy was strongly associated with development of overt thyrotoxicosis (OR 10.8, 95% CI 4.51-25.6 vs. CTLA-4 monotherapy; p<0.001), as was female sex (OR 2.02, 95% CI 1.37-2.95; p<0.001) and younger age (OR 0.83 per 10-years, 95% CI 0.72-0.95; p=0.007). By comparison, median onset of overt hypothyroidism was 14 weeks (IQR 8-25). The frequency of overt hypothyroidism did not differ between different ICI-types. The strongest associations for hypothyroidism were higher baseline TSH (OR 2.33 per mIU/L, 95% CI 1.61-3.33; p<0.001) and female sex (OR 3.31, 95% CI 1.67-6.56; p=0.01). Overt thyrotoxicosis was associated with longer progression free survival (HR 0.68, 95% CI 0.49-0.94; p=0.02) and overall survival (HR 0.57, 95% CI 0.39-0.84; p=0.005). There was no association between hypothyroidism and cancer outcomes. Conclusions Thyroid irAEs are common and there are multiple distinct phenotypes. Different thyroid irAE subtypes have unique clinical and biochemical associations, suggesting potentially distinct etiologies for thyrotoxicosis and hypothyroidism arising in this context.

Context Checkpoint inhibitor–associated autoimmune diabetes mellitus (CIADM) is a rare illness, and little is known about its incidence, clinical features, or pathogenesis. Case Series Description Consecutive patients from a single quaternary melanoma center who developed new-onset insulin-requiring diabetes after commencing anti–programmed cell death-1 (PD-1) immunotherapy were studied to describe CIADM characteristics. Ten (1.9%) of 538 patients with metastatic melanoma treated with anti–PD-1–based immunotherapy from March 2015 to March 2018 developed CIADM. Nine patients had no history of diabetes, and one had pre-existing type 2 diabetes mellitus. Median time from immunotherapy start to CIADM diagnosis was 25 weeks [interquartile range (IQR), 17.5 to 34.5 weeks]. All patients had normal serum C-peptide shortly before CIADM onset and an inappropriately low level when measured soon after. At CIADM diagnosis, median hemoglobin A1c was 7.6% (IQR, 7.15% to 9.75%), median glucose level was 32.5 mmol/L (IQR, 21.6 to 36.7 mmol/L), and median C-peptide concentration was 0.35 nmol/L (IQR, 0.10 to 0.49 mmol/L). Type 1 diabetes (T1D)–associated autoantibodies (DAAs) were present in two patients (both of whom had anti–glutamic acid decarboxylase antibody); all were negative for insulin-associated protein 2, insulin, and ZnT8. Three patients were heterozygous for an HLA class II T1D-risk haplotype; two additional patients also carried protective haplotypes for T1D. All patients continued immunotherapy; eight (80%) had complete or partial oncological response, and all patients required ongoing insulin therapy. Conclusion CIADM is characterized by sudden permanent β-cell failure occurring after immunotherapy. It is distinct from T1D, usually lacks DAA or T1D-associated HLA-risk haplotypes, and is associated with difficult glycemic control from the onset. As such, CIADM represents a new model of auto-inflammatory β-cell failure.

Combination immunotherapy has a greater risk of development of endocrinopathy compared to anti-PD-1 monotherapy. Regular biochemical profiling of patients, particularly within the first twelve weeks, results in early detection of endocrinopathy to minimise morbidity.