HMBS and neoplasm: To synthesize one molecule of protoporphyrin IX (PpIX), eight 5-ALA molecules are needed; separate steps of heme synthesis provoke catalyzation of special enzymes, among which ferrochelatase (or protoporphyrin ferrochelatase) and porphobilinogen deaminase are specially interesting, as their activity is increased in tumor cells compared to normal brain tissues (32).