In this study, we not only reveal that endothelial cells (ECs) are strongly associated with the progress of papillary thyroid cancer (PTC) using single-cell RNA-seq (scRNA-seq) data downloaded from Gene Expression Omnibus (GEO) and WGCNA, but also screen 5 crucial genes of ECs:CLDN5,ABCG2,NOTCH4,PLAT, andTMEM47. The gene discussed is CLDN5; the disease is thyroid gland papillary carcinoma.