Evaluation of CTLA-4 and PD-L1 Expression in Thyroid Carcinoma and Its Prognostic Significance

Introduction Immune checkpoint inhibitors (ICIs) targeting cytotoxic T-lymphocyte-associated antigen-4 (CTLA-4) and programmed death-ligand 1 (PD-L1) have revolutionised treatment and improved outcomes in various malignancies. We aimed to evaluate CTLA-4 and PD-L1 immunoexpression in thyroid tumours and correlated them with clinicopathological parameters. Methods The study included 90 cases of thyroid malignancies comprising papillary thyroid carcinoma (PTC) (n = 64, 54.2%), follicular thyroid carcinoma (FTC) (n = 19, 16.1%), anaplastic thyroid carcinoma (ATC) (n = 3, 2.5%), and poorly differentiated carcinoma (n = 4, 3.4%), two cases (1.69%) of non-invasive follicular thyroid neoplasm with papillary-like nuclear features (NIFTP) along with 26 cases (22%) of benign thyroid lesions. CTLA-4 (UMAB249) and PD-L1 (SP263) expression were assessed in all the cases of thyroid tumours. Results were compared with clinicopathologic parameters and overall survival. Results PD-L1 was positive in all three cases of anaplastic thyroid carcinoma (ATC), 33% (n = 21) cases of PTC, and 16% (n = 3) cases of FTC. PD-L1 positivity was significantly associated at tumour proportion score (TPS) ≥1% with lymphovascular invasion and age ≤40 years and at TPS ≥50% with tumour necrosis and N-stage. Immune proportion score (IPS) did not correlate with any clinicopathological parameters except for the N-stage. CTLA-4 was positive in six cases of PTC (1-5%); five showed lymph node involvement (p = 0.032). IPS was positive in 14 cases, and a significant association was seen with lymph node metastasis, lymphocytic infiltration, and lymphovascular invasion. Three cases of PTC showed co-expression for PD-L1 and CTLA-4 in tumour cells. No significant association was seen between PD-L1 expression and survival. Conclusion The current data suggest that PD-L1 is expressed in differentiated thyroid carcinoma, mainly PTC and ATC, indicating higher responsiveness to immunotherapy. A subset of PTC showed co-expression of PD-L1 and CTLA-4. These findings suggest the need for further investigation to utilise combinational immunotherapy, including anti-PD-L1 and anti-CTLA-4.