An excess of patients with non-sigmoid colon cancer carrying the combined genotype CYP3A4*1A/*1B plus CYP3A5*3/*3 was observed as compared to healthy subjects (Chi-square = 10.3, p = 0.0015, non significant in multiple comparison analyses) With regard to allele frequencies, CYP3A4*1B allele frequency was 6.6%, 5.9% and 1% and CYP3A5*3 frequency was 91.1%, 90.1% and 93.6% among patients with non-sigmoid colon, sigmoid colon and rectum, respectively. This evidence concerns the gene CYP3A5 and malignant colon neoplasm.