In a randomized , cross-over , placebo-controlled trial of @ healthy men and women , homozygous for UGT@A@ * @ or UGT@A@ * @ , we explored differences between global epithelial and stromal expression , using Affymetrix U@ +@ microarrays and tested effects of @-day aspirin supplementation ( @ mg/d ) on epithelial and stromal gene expression and colon prostaglandin E@ ( PGE@ ) levels .