The first experiments conducted on colorectal cancer cell lines and in the mouse xenograft model led to the discovery that POX/PRODH is p53-induced gene-6 (PIG-6), which acts as a tumor suppressor, and this suppression depends on the quantity of the enzyme—high levels of POX/PRODH expression lead to apoptosis, while lower levels cause cell cycle arrest in the G2 phase and inhibit proliferation [8,77]. The gene discussed is PRODH; the disease is neoplasm.