CHI3L1 and bladder transitional cell carcinoma: Aiming at CHI3L1, the highest fold change value among differentially expressed genes in the highly malignant cell subsets found by scRNA-seq analysis in the clinical PTC tissues, we further performed GSEA based on the TCGA database and found that CHI3L1 mRNA was highly expressed in various malignant tumors such as bladder urothelial carcinoma, colon cancer, esophageal cancer, breast invasive carcinoma, head and neck squamous cell carcinoma, renal clear cell carcinoma, and lung adenocarcinoma (Fig. 5A).