Association between the type of thyroid dysfunction induced by immune checkpoint inhibitors and prognosis in cancer patients

Background: Immune checkpoint inhibitors (ICIs) cause thyroid immune-related adverse effects (irAEs). However, associations between each type of thyroid immune-related adverse effect (irAE) and the anti-tumor effect of ICI remains unknown. This study aimed to determine the effects of each type of thyroid dysfunction on patient survival. Methods: Patients who initiated ICI treatment from January 2015 to December 2019 in Seoul St. Mary’s Hospital were retrospectively analyzed. Thyroid dysfunction was classified into four types: newly developed overt or subclinical hypothyroidism, thyrotoxicosis, worsened hypothyroidism, and subclinical hyperthyroidism. Patients were divided into two groups according to the presence or absence of thyroid dysfunction. Results: Among the 191 patients, 64 (33.5%) developed thyroid irAEs. There was no significant difference in age, sex, or cancer type between the two groups. The overall survival in patients with thyroid irAEs was significantly higher than that in patients without thyroid irAEs (25 months vs. 18 months, respectively, p = 0.005). After adjusting for confounding factors, the hazard ratio for mortality in the thyroid irAE group compared to the no thyroid irAE group was 0.480 (p = 0.006). Newly developed overt or subclinical hypothyroidism patients showed a significantly lower hazard ratio for mortality of 0.324 (p = 0.002). Patients with thyrotoxicosis showed a worse hazard ratio for mortality than those without thyroid irAE, although the difference was not statistically significant. Conclusions: It was verified that ICI treatment-induced thyroid dysfunction was associated with better survival, even in the real-world practice. Thus, endocrinologists should cooperate with oncologists to monitor patients treated with ICIs.