Prostaglandin E2, a bioactive lipid targeted by aspirin and COX-2.selective inhibitors, has previously been shown to promote cancer progression. Prostaglandin dehydrogenase(PGDH) catalyzes the rate-limiting step of Prostaglandin E2 catabolism in vivo Here we show Pgdh expression by in situ hybridization of ApcMin intestine, a mouse model of polyp formation. Pgdh is strongly expressed in normal tissue and much reduced in preinvasive adenomatous polyps, demarcated by a dotted line. This data supports a novel,COX-2.independent mechanism for accumulation of Prostaglandin E2 in colorectal cancer. For details, see the article by Mann et al. on page 6649 of this issue.