Porphobilinogen synthase is the crucial first step of tetrapyrrole biosynthesis which tetrapyrroles like unconjugated bilirubin, bilirubin ditaurate, biliverdin, biliverdin-/bilirubin dimethyl ester, urobilin, stercobilin, and protoporphyrin exhibited DNA-damaging and apoptosis in colon and liver cancer cells [113, 114]. This evidence concerns the gene ALAD and liver cancer.