Low Free Triiodothyronine and Immune-Related Hyperthyroidism Are Associated with Overall and Progression-Free Survival in Head and Neck Squamous Cell Carcinoma Treated with Pembrolizumab.

Introduction: Thyroid function is frequently impaired in recurrent/metastatic head and neck squamous cell carcinoma (R/M HNSCC). In patients treated with pembrolizumab, immune-related adverse events (irAEs) of the thyroid are common. However, the prognostic significance of baseline and on-treatment thyroid dysfunction is currently unclear.Methods: This study included 95 patients who received pembrolizumab for R/M HNSCC between 2016 and 2022. Baseline thyroid status, according to serum hormone levels, and irAEs were assessed. Univariable and multi variable Cox regression analyses were performed for overall survival (OS) and progression-free survival (PFS). Furthermore, the best overall response according to the prognostic groups was examined.Results: Low fT3 (HR: 2.52, p = 0.006), immune-related hyperthyroidism (HR: 0.11, p = 0.038), ECOG performance status & GE;2 (HR: 3.72, p = 0.002), and platinum-refractory disease (HR: 3.29, p = 0.020) were independently associated with OS. Furthermore, immune-related hyperthyroidism was associated with longer PFS (HR: 0.13, p = 0.007), a higher objective response rate (83% vs. 31%, p = 0.018), and a higher disease control rate (100% vs. 43%, p = 0.008). Thyroid-related autoantibodies were elevated in 40% of thyroid irAEs cases with available measurements. Out of 16 thyroid irAEs, 15 occurred in patients with fT3 above the lower limit of normal.Conclusion: Low fT3 was associated with worse OS. Immune-related hyperthyroidism was correlated with both improved OS and PFS. Baseline fT3 assessment and close on-treatment monitoring of serum thyroid levels may be valuable for risk stratification in R/M HNSCC patients receiving pembrolizumab.