THE POLYP PREVENTION TRIAL-I - RATIONALE, DESIGN, RECRUITMENT, AND BASE-LINE PARTICIPANT CHARACTERISTICS

The Polyp Prevention Trial (PPT) is a multicenter randomized controlle d trial examining the effect of a low-fat (20% of total energy intake) , high-fiber (18 g/1000 kcal), high-vegetable and -fruit (5-8 daily se rvings) dietary pattern on the recurrence of adenomatous polyps of the large bowel, precursors of most colorectal malignancies. Eligibility criteria include one or more adenomas removed within 6 months of rando mization; complete nonsurgical polyp removal and complete colonic exam ination to the cecum at the qualifying colonoscopy; age 35 years or mo re; no history of colorectal cancer, inflammatory bowel disease, or la rge bowel resection; and satisfactory completion of a food frequency q uestionnaire and 4-day food record. Of approximately 38,277 potential participants with one or more polyps recently resected, investigators at eight clinical centers randomized 2,079 (5.4%; 1,037 in the interve ntion and 1,042 in the control arm) between June 1991 and January 1994 , making the PPT the largest adenoma recurrence trial ever conducted. Of PPT participants, 35% are women and 10% are minorities. At study en try, participants averaged 61.4 Sears of age; 14% of them smoked, and 22% used aspirin. At the baseline colonoscopy, 35% of participants had two or more adenomas, and 29% had at least one large (greater than or equal to 1 cm) adenoma. Demographic, behavioral, dietary, and clinica l characteristics are comparable across the two study arms. Participan ts have repeat colonoscopies after 1 (T-1) and 4 (T-4) years of follow -up. The primary end point is adenoma recurrence; secondary end points include number, size, location, and histology of adenomas. All resect ed lesions are reviewed centrally by gastrointestinal pathologists. Th e trial provides 90% power to detect a reduction of 24% in the annual adenoma recurrence rate. The primary analytic period, on which sample size calculations were based, is 3 years (T-1 to T-4), which permits a 1-year lag time for the intervention to work and allows a more defini tive clearing of lesions at T-1, given that at least 10-15% of polyps may be missed at baseline, The final (T-4) colonoscopies are expected to be completed in early 1998.