COL4A1 and hepatocellular carcinoma: In 50 paired HCC and normal liver samples from TCGA dataset, COL1A1 and COL1A2 were only upregulated in 74% (37 of 50) of HCC samples, but COL4A1 and COL4A2 were upregulated in 100% (50 of 50) of HCC samples (Additional file 4: Figure S1A).