High Expression of Immune Checkpoint Molecules in Different Types of Thyroid Cancer

This study aimed to investigate the expression of programmed cell death protein-1 (PD-1) and its ligand (PD-L1) immune checkpoint molecules in thyroid carcinomas and determine their association with the clinicopathological characteristics of patients. Thyroid tissue specimens from 100 patients diagnosed with primary thyroid carcinomas including papillary thyroid carcinoma (PTC), follicular thyroid carcinoma (FTC), medullary thyroid carcinoma (MTC), and anaplastic thyroid carcinoma (ATC) were collected. Sections were prepared from formalin-fixed paraffin-embedded samples, and PD-1 and PD-L1 expressions were examined using immunohistochemistry. PD-1 was detected in tumor-infiltrating lymphocytes (TILs) in 88% of the patients and tumor cells in 28% of the patients with 10% in PTC, 5% in FTC, 5% in MTC, and 8% in ATC). PD-L1 was found in tumor cells and TILs in 30% and 79% of the patients, respectively. Moreover, a significant difference was observed in PD-1 and PD-L1 expression between tumor cells and TILs across different tumor types. However, their expression in tumor cells and TILs was significantly higher in ATC compared to other tumor types. Additionally, the expression of PD-1 and PD-L1 was significantly associated with an advanced stage, higher tumor size, tumor necrosis, and mitosis. A significant positive correlation was also observed between the expression of PD-1 and PD-L1 in tumor cells and TILs. The higher expression of PD-1 and PD-L1 may contribute to tumor progression. Therefore, combinational immunotherapy by these immune checkpoint inhibitors might be a promising strategy for clinical improvement in patients with thyroid cancer, especially those with ATC.