PGK1 and malignant colon neoplasm: The last reference gene, the glycolysis enzyme phosphoglycerate kinase 1 (PGK1), is a target gene of both the myc oncogene pathway and the hypoxia inducible factor 1α (HIF-1α) and is therefore considered as a marker gene for a number of malignant tissues such as kidney cancer [9] or colon cancer [10].