Evaluation of GARP immunohistochemical expression in papillary thyroid carcinoma

Background Glycoprotein A repetitions predominant (GARP) is a novel transmembrane protein highly expressed on the surface of regulatory T cells (Tregs), which are a subset of immunosuppressive T lymphocytes that play a major role in inhibiting the antitumor immune response. Many studies documented increased GARP expression in various tumors, which is related to a poorer prognosis, and only one single paper investigated its expression in thyroid tumors. Aim To evaluate the immunohistochemical expression of GARP in differentiated thyroid carcinomas and their tumor-infiltrating lymphocytes (TILs) in comparison to its expression in other benign and low-risk lesions. Methods Sixty-nine cases of different thyroid lesions were subgrouped into 37 cases of malignant thyroid neoplasms, 25 cases of benign thyroid lesions, and 7 cases of low-risk neoplasms collected from the Pathology Department Laboratories of Ain Shams University Hospitals during the period from January 2017 to December 2021 and stained immunohistochemically for GARP. Immunohistochemical (IHC) results were evaluated in thyroid epithelial cells and TILs. The expression of GARP was correlated with the different clinicopathological parameters. Results GARP expression discloses a significant statistical difference between the three studied groups (P < 0.001). High GARP expression was detected in 89.19% of the malignant cases and in 28.57% of low-risk neoplasms, while all benign lesions exhibited low GARP expression. High GARP expression of TILs was detected in 60% of the malignant cases. Synchronous high GARP expression in tumor tissue and in the surrounding TILs was detected in 63.16% of the malignant cases, yet these results did not reach statistical significance. Conclusion GARP is a marker of Tregs, whose high expression is increased in malignant over benign and low-risk lesions. It might be a potential novel target for anticancer immunotherapy.