SFRP4 and neoplasm: Using the Human Protein Atlas database, in terms of single cell type specificity, we found that SFRP2 is specifically expressed in the fibroblasts (https://www.proteinatlas.org/ENSG00000145423-SFRP2/celltype), but SFRP4 is specifically expressed in the peritubular cells (https://www.proteinatlas.org/ENSG00000106483-SFRP4/celltype), suggesting that the contribution of tumor stroma to UC development is more likely to be mediated by SFRP2.