Evaluation of GARP Immunohistochemical Expression in Papillary Thyroid Carcinoma

Abstract Background Glycoprotein A repetitions predominant (GARP) is a novel trans-membrane protein, highly expressed on the surface of regulatory T cells (Tregs). Tregs are a subset of immunosuppressive T-lymphocytes that play a major role in inhibiting antitumor immune response. Many studies documented increased GARP expression in various tumors. Our study was designated to evaluate the immunohistochemical (IHC) 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 and to assess the potential diagnostic role of GARP IHC expression in different thyroid lesions. Material and Methods Sixty-nine cases of different thyroid lesions subgrouped into: 37 cases of malignant thyroid neoplasms, 25 cases of benign thyroid lesions and 7 cases of low-risk neoplasms collected from pathology department laboratories of Ain Shams university hospitals during the period from January 2017 to December 2021 and stained immunohistochemically for GARP. IHC expression of GARP was evaluated in thyroid epithelial cells and TILs. The expression of GARP was correlated with the different clinicopathological parameters. Results GARP expression discloses 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. No statistically significant correlation was detected between GARP expression and patient’s age or sex, as well as tumor focality, extrathyroid extension, and cervical lymph node metastasis (MTs). 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, this result didn’t 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.