CPOX and central nervous system cancer: Numerous studies have correspondingly reported correlations of tumor fluorescence with expression or activity of FECH or other key enzymes of the heme biosynthesis pathway (e.g., coproporphyrinogen-Oxidase, CPOX) or transmembrane transporters (e.g., ATP-binding cassette super-family B member 6, ABCB6 or ATP-binding cassette super-family G member 2, ABCG2) of PpIX in gliomas [6,7,8,9,10,11,12].