PYCR1 and cancer: The majority of the experimental evidence that associates the metabolism of L-proline to cancer development revolves around the two genes that catalyze the last step in L-proline biosynthesis and the first step of its catabolism, namely PYCR1 and PRODH1. A simplified view of those genes’ modus operandi in cancer would implicate proline biosynthesis by the PYCR enzymes in cancer progression and its catabolism by PRODH in the suppression of tumorigenesis.