CYP3A5 and cancer: The CYP3A5 gene encodes a member of the cytochrome P450 (CYP) superfamily of enzymes, which are monooxygenases that catalyze many reactions involved in drug metabolism and in the synthesis of cholesterol, steroids, and other lipids.1, 2, 3, 4 The 3A subfamily of CYPs (CYP3A) is critical for xenobiotic clearance in humans and is reported to metabolize more than half of all currently prescribed drugs.5, 6, 7 Recently, studies of CYP3A5 have addressed the relation of CYP3A5 single-nucleotide (or genotype) polymorphism to cancer risk or drug metabolism.6