SFRP2 and bladder transitional cell carcinoma: Using the Tumor Immune Estimation Resource (TIMER) database version 2.0 (28), which integrates the TCGA data, we observed that both the SFRP1 and SFRP2 transcripts are significantly negatively correlated with tumor purity (the percentage of cancer cells in a sample) and positively correlated with cancer-associated fibroblast (CAF) infiltration in bladder urothelial carcinoma, but the SFRP2 gene showed a more distinguished correlation (Supplementary Figure 2 and Figure 2C).