In contrast, when the study group subjects included those with familial adenomatous polyposis, the chemopreventive effects of daily aspirin were present in both those with and without a copy of CYP2A6*1. We report herein that the CYP2A6 wild-type allele could be a candidate biomarker for reduced chemopreventive effects of daily aspirin in a population with a wide range of CYP2A6 phenotypes including high frequencies of phenotypes with impaired activities caused by variations and whole-gene deletions. This evidence concerns the gene CYP2A6 and Familial adenomatous polyposis.