Adequacy of Immune Checkpoint Inhibitor-Associated Thyroid Function Monitoring After Therapy.

[PURPOSE] Immune checkpoint inhibitor (ICI)-induced thyroid dysfunction is a common endocrine immune-related adverse event. Although rates during therapy are well documented, data on post-treatment thyroid dysfunction are limited. We hypothesized that post-ICI thyroid dysfunction is under-recognized because of inadequate surveillance.

[METHODS] A retrospective analysis of 3,626 patients treated with ICIs for various malignancies within a single health system was conducted. Clinically acted-upon thyroid dysfunction (diagnosis or thyroid-directed medication) was evaluated before, during, and after ICI therapy, alongside rates of thyroid laboratory surveillance.

[RESULTS] Clinically acted-upon thyroid dysfunction occurred in 8.1% (294/3,626) during treatment and 4.4% (159/3,626) after treatment. Among the 1,170 patients with post-ICI thyroid laboratory results and no prior dysfunction, 11.6% (136/1,170) developed post-ICI thyroid dysfunction. However, 48.6%% (1,764/3,626) had no post-ICI thyroid laboratory results. Thirty percent of patients with abnormal thyroid stimulating hormone (TSH) values and no clinically acted-upon thyroid dysfunction before therapy discontinuation subsequently developed clinically acted-upon thyroid dysfunction, and the rate of post-ICI clinically acted-upon thyroid dysfunction was higher in patients who received 9 or less months of ICI therapy.

[CONCLUSION] Post-ICI thyroid dysfunction is frequent, with 11.6% of monitored patients being affected, and patients with abnormal TSH before ICI discontinuation and those who received treatment for 9 months or less may benefit from more stringent post-ICI surveillance.