Adequacy of immune checkpoint inhibitor-associated thyroid function monitoring following therapy.

12116 Background: Immune checkpoint inhibitor (ICI)-induced thyroid dysfunction is the most common endocrine immune-related adverse event. While ICI-induced thyroid dysfunction rates during therapy are well documented, data on post-treatment dysfunction is limited. Describing these rates is important as ICIs are increasingly used in the curative treatment setting. This study aimed to evaluate the rates of post-ICI thyroid dysfunction, evaluate for predictors of post-ICI thyroid dysfunction and assess adequacy of post-ICI thyroid function surveillance. Methods: A retrospective analysis of 3626 patients treated with ICIs for various malignancies and cancer stages within a single health system from March 2013 to December 2022 was conducted. Rates of clinically acted upon thyroid dysfunction (diagnosis or thyroid-directed medication) were evaluated before, during, and after ICI therapy, alongside rates of thyroid laboratory surveillance in the post treatment setting. A multivariate analysis evaluated the odds of developing clinically acted upon post-ICI thyroid dysfunction based on patient/treatment characteristics. Rates of clinically acted upon thyroid dysfunction were evaluated based on therapy duration. Statistical analyses were carried out using R V4.1.0. Results: Clinically acted upon thyroid dysfunction occurred in 8.1% of patients (294/3626) during treatment and 4.4% (159/3626) after treatment. However, in patients alive two months after ICI cessation, 53.9% (989/1834) had no post-ICI thyroid function tests performed. Among the 1170 patients with post-ICI thyroid labs and no prior dysfunction, 11.6% (136/1170) developed post-ICI thyroid dysfunction. Thirty percent of patients with abnormal TSH values and no clinically acted upon thyroid dysfunction prior to therapy discontinuation subsequently developed clinically acted upon thyroid dysfunction. The rate of post treatment thyroid dysfunction in patients who underwent thyroid test surveillance and received <9 months of therapy was 13.3% compared to 6.5% in those who received therapy >9 months. The odds ratio for developing post-ICI dysfunction were 1.76 (95% CI, 1.03 to 2.95) for patients with urologic malignancies compared to patients with respiratory malignancies as the reference group. Conclusions: Post-ICI thyroid dysfunction is frequent, with 11.6% of patients who undergo thyroid function surveillance being affected. Patients with abnormal TSH before ICI discontinuation and those who received treatment for < 9 months as well as those with urologic malignancies may benefit from more stringent post-ICI surveillance.