Photodynamic diagnosis, a technique used for the cancer diagnosis, has also shown the reduced accumulation of metabolized photosensitizer PpIX from 5-ALA, due to decreased expression of protoporphyrinogen IX oxidase (PPOX) and coproporphyrinogen oxidase (CPOX) enzymes involved in PpIX synthesis [47,48]. The gene discussed is CPOX; the disease is cancer.