Muir CA, Clifton-Bligh RJ, Long GV, et al. - Researchers undertook this retrospective cohort investigation to determine thyroid immune-related adverse events (irAEs) after immune checkpoint inhibitor (ICI) treatment as well as to analyze their clinical and biochemical links. Participants were patients suffering from melanoma receiving CTLA-4 and/or PD-1 based ICI treatment from Nov 1, 2009 to Dec 31, 2019. Of 1246 patients, an ICI-associated thyroid irAE occurred in 518 (42%) patients. The most common thyroid irAE was subclinical thyrotoxicosis (n = 234), followed by overt thyrotoxicosis (n = 154), subclinical hypothyroidism (n = 61), and overt hypothyroidism (n = 39). Combination immunotherapy was found to be strongly related to occurrence of overt thyrotoxicosis, as was female gender and younger age. For hypothyroidism, the strongest links were higher baseline TSH and female gender. Longer progression free survival as well as overall survival were observed in relation to overt thyrotoxicosis. No link was identified between hypothyroidism and cancer outcomes. Overall, findings revealed a common occurrence of thyroid irAEs, with multiple distinct phenotypes observed. Unique clinical as well as biochemical links of different thyroid irAE subtypes were revealed, indicating potentially distinct causes for thyrotoxicosis and hypothyroidism originating in this context.