<p>Despite the discoveries of new and promising therapeutics, effective treatments for advanced and metastatic thyroid cancer (THCA) are still lacking. Epithelial-to-mesenchymal transition (EMT) is crucial for developing an invasive phenotype in tumor cells and, therefore, a hallmark of metastatic disease. We here investigate the effect of EGF-like repeat and discoidin I-like domain-containing protein 3 (EDIL3) on EMT in THCA and the mechanism involved. THCA cells with EDIL3 knockdown were generated to analyze the effect on EMT, proliferation, migration, invasion, and angiogenesis. THCA cells with knockdown of EDIL3 had increased expression of E-cadherin and decreased expression of Vimentin and Slug, proliferation, migration, invasion, and angiogenesis. GLI-similar 2 (GLIS2) bound to the EDIL3 promoter to activate its expression. Knockdown of GLIS2 promoted the killing activity of CD8⁺ T cells, while overexpression of EDIL3 reversed phenotypic changes and suppressed the anti-tumor responses of T cells. Overexpression of EDIL3 also reversed the inhibitory effects of knocking down GLIS2 alone on tumor metastasis in BALB/c nude mice. Together, our results demonstrate that EDIL3 induced by GLIS2 inhibits the anti-tumor activity of CD8⁺ T cells and promotes EMT in THCA.</p>