Expression analysis using RT-qPCR revealed significant (p-value < 0.05) down-regulation of BRAF, EIF1 AX, FOXE1, KRAS, PDGFRA, PIK3 CA, PTEN, and TERT genes in thyroid cancer cell lines compared to controls, with ROC curves indicating high diagnostic accuracy (AUC 0.93–0.99). The gene discussed is PTEN; the disease is thyroid cancer.