Prevention of Progression of Duodenal Adenomas in Patients With Familial Adenomatous Polyposis

Inclusion Criteria: * Patients with Familial adenomatous Polyposis: APC-mutation identified or more than 100 colorectal polyps on diagnosis * Spigelman score of duodenal adenoma equal to II or III Exclusion Criteria: * Incapability of signing informed consent * Active gastric or duodenal ulcer, gastrointestinal bleeding * Cardiovascular disease or risk: * Congestive cardiac failure: NYHA class II to IV * Proven ischemic heart disease and/or cerebrovascular disease * Risk factors: hypertension, hyperlipidaemia, diabetes mellitus, family history of cardiovascular events (≥2 first degree family members \<55 years) * Renal dysfunction: creatinine clearance below 50mL/min * Liver dysfunction: albumin below 25 g/L or Child-Pugh-score equal to or below 10 * Known allergic reaction to sulfonamides, NSAIDs or ursodeoxycholic acid * Use of NSAIDs or ursodeoxycholic acid for more than 1 week during the 6 months prior to the start of the study * Use of lithium * Symptomatic gallstones * Inflammatory bowel disease * (Possible) pregnancy or breast feeding