Familial adenomatous polyposis (FAP) leads to adenomas and eventual adenocarcinomas in colon and less frequently, duodenum. Chemopreventive strategies have been studied in FAP patients to delay the development of adenomas and cancers. The non-steroidal anti-inflammatory drugs (NSAIDs) and selective cyclooxygenase-2 inhibitor have shown the regression of colorectal and duodenal adenomas in FAP patients. However, these drugs showed gastrointestinal damage and cardiovascular risks, and new preventive strategies are needed. Niclosamide, an anti-helminthic drug, has recently been suggested to have a suppressive effect on tumorigenesis via inhibition of Wnt pathway, and have no significant safety issues. The investigators devised a double-blind randomized controlled trial to evaluate the effect of niclosamide on polyps of colorectum and duodenum in FAP patients.

This clinical trial is a double-blind randomized controlled trial to evaluate the effect of niclosamide on polyps of colorectum and duodenum in FAP patients. FAP patients, satisfied an enrollment criteria, will be randomly assigned in a 2:1 ratio to receive niclosamide (650 mg) or placebo tablets orally once a day for 6 months. The base-line and six-month endoscopic examination (colonoscopy/sigmoidoscopy and upper gastrointestinal endoscopy) will be recorded, and photographs will be taken at the tattoo-marked area. The number and size of polyps, and a qualitative assessment of the total extent of polyposis will be measured. If there is no significant improvement in any of the 12 initial cases (niclosamide 8: placebo 4), this trial will be discontinued.

Inclusion Criteria:

• Patients with familial adenomatous polyposis(FAP) who are 20 to 65 years of age.
• FAP patients who have colonic or duodenal polyp.
• FAP patients who have five or more polyps 2mm or more in diameter in endoscopic examination.

Exclusion Criteria:

• FAP patients who had a history of colectomy within the previous 12 months or need to undergo colectomy within 8 months after randomization.
• FAP patients with malignant disease, including colorectal cancer.
• FAP patients who used NSAIDs (non-steroidal anti-inflammatory drugs) or aspirin three or more times a week within 6 months of randomization.
• Pregnant or breast-feeding patients. 6. Patients with abnormal results of serum laboratory tests (renal function and liver function test).

double blind randomized