Because CYP3A activity is a major determinant of drug response and may be associated with risk for cancers such as breast and prostate cancer (Keshava et al. 2004), the identification of sequence variants at the CYP3A locus and functional characterization of their clinical relevance have been of long-standing interest in pharmacogenetics and toxicogenetics. This evidence concerns the gene CYP3A4 and prostate carcinoma.