Phenotypic Differences in Thyroid Immune Related Adverse Events Following Treatment With Immune Checkpoint Inhibitors

Background: Thyroid toxicity is common following immune checkpoint inhibitor (ICI) treatment. Published studies estimate the incidence at 10-20%, although rates vary widely between different ICIs. The etiology of ICI-associated thyroid immune related adverse events (irAEs) is unknown & not all patients develop a classic thyroiditis-like presentation of transient hyperthyroidism followed by a hypothyroid phase. Only small observational cohorts have been reported & the clinical & biochemical features of thyroid irAEs have not been well characterized. The current study aimed to describe thyroid irAEs in a large cohort of patients with melanoma. Methods: We reviewed outcomes in a prospective cohort of adult patients undergoing ICI treatment for advanced melanoma. Thyroid function was measured at baseline & at regular intervals during treatment. Thyroid irAEs were defined as new biochemical thyroid dysfunction developing over the course of routine follow-up. Results: Thyroid irAEs occurred in 518 of 1246 (42%) patients. Median follow-up was 11.3 months. Multiple patterns of thyroid-irAEs were observed, such as hyperthyroidism (subclinical or overt) in 31%, hypothyroidism in 8%, & euthyroid hyperthyroxinemia, hypothyroxinemia & isolated low FT3 syndrome each in 1% of participants. Thyroid irAEs were more frequent following combination (CTLA-4 + PD-1) ICI treatment (56%) than following PD-1 (38%) or CTLA-4 (25%) based monotherapies (p=0.001). The severity of thyroid irAEs differed by ICI, with higher rates of overt (vs. subclinical) thyroid dysfunction following combination ICI treatment (47%) relative to PD-1 (37%) & CTLA-4 (19%) monotherapies (p=0.001). Younger age (OR 0.88 per 10-yrs; 95% CI 0.81-0.96), female sex (OR 1.62; 95% CI 1.27-2.08) & combination ICI-treatment (vs. CTLA-4, OR 3.76, 95% CI 2.49-5.75; vs. PD-1, OR 1.90, 95% CI 1.45-2.49) were associated with higher odds of thyroid irAE. Time to onset of thyroid dysfunction was shorter in patients with overt hyperthyroidism relative to other types of thyroid irAE (log rank p=0.001). Overt hyperthyroidism was associated with increased irAEs in other organ systems (colitis, hepatitis, etc), increased irAE severity & increased multi-system irAEs than euthyroid patients or patients with other subtypes of thyroid irAE (p=0.003). Overt hyperthyroidism was also associated with improved progression free survival (HR 0.57; 95% CI 0.39-0.84; p=0.005) & overall survival (HR 0.68; 95% CI 0.49-0.94; p=0.02). No benefit to cancer survival was observed with other thyroid irAE subtypes. Conclusions: Thyroid irAEs were common. Combination ICI treatment resulted in more frequent, more severe, & earlier onset thyroid irAEs. Of thyroid irAE subtypes, overt hyperthyroidism was uniquely associated with increased immune responsiveness, as evidenced by higher incidence of extra-thyroidal irAEs & improvements in cancer survival.