To explore a clinical connection between collagen I (COL1) and tumor cell invasion, we evaluated collagen I gene expression (COL1A1 and COL1A2) in correlation to tumor staging in three independent cohorts of bladder cancer patients [kim, n = 16520, Riester, n = 9321 and The Cancer Genome Atlas (TCGA), n = 37622] (Fig. 1a, b). This evidence concerns the gene COL1A2 and urinary bladder cancer.