COL6A2 and urinary bladder cancer: It has been revealed that COL1A1 protein was markedly upregulated in MIBC, which could activate the epithelial–mesenchymal transition and TGF-β signaling pathway contributing to the proliferation and invasion of bladder cancer cells (44), whereas the significantly downregulated expression of collagen type IV-α1 and α2 (COL6A1 and COL6A2) was found to promote tumor progression in both the NMIBC and MIBC tissue samples (45).