The polyp prevention trial I: rationale, design, recruitment, and baseline participant characteristics.
The Polyp Prevention Trial (PPT) is a multicenter randomized controlled 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 servings) 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 randomization; complete nonsurgical polyp removal and complete colonic examination to the cecum at the qualifying colonoscopy: age 35 years of more; no history of colorectal cancer, inflammatory bowel disease, or large bowel resection; and satisfactory completion of a food frequency questionnaire 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 intervention 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 entry, participants averaged 61.4 years 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 (> of = 1 cm) adenoma. Demographic, behavioral, dietary, and clinical characteristics are comparable across the two study arms. Participants 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 resected lesions are reviewed centrally by gastrointestinal pathologists. The 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 definitive 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.
Schatzkin
A
A
National Cancer Institute, Bethesda, Maryland, USA.
Lanza
E
E
Freedman
L S
LS
Tangrea
J
J
Cooper
M R
MR
Marshall
J R
JR
Murphy
P A
PA
Selby
J V
JV
Shike
M
M
Schade
R R
RR
Burt
R W
RW
Kikendall
J W
JW
Cahill
J
J
D000236:Adenoma / Q000178:diet therapy / Q000517:prevention & control / Q000601:surgery; D018256:Adenomatous Polyps / Q000178:diet therapy / Q000517:prevention & control* / Q000601:surgery; D000328:Adult; D001241:Aspirin / Q000627:therapeutic use; D003110:Colonic Neoplasms / Q000178:diet therapy / Q000517:prevention & control; D003111:Colonic Polyps / Q000178:diet therapy / Q000517:prevention & control* / Q000601:surgery; D003113:Colonoscopy; D003710:Demography; D018752:Diet, Fat-Restricted; D004043:Dietary Fiber / Q000008:administration & dosage; D002149:Energy Intake; D005260:Female; D005500:Follow-Up Studies; D005638:Fruit; D006801:Humans; D008297:Male; D008875:Middle Aged; D008913:Minority Groups; D009364:Neoplasm Recurrence, Local; D018579:Patient Selection; D011230:Precancerous Conditions / Q000178:diet therapy / Q000517:prevention & control; D012107:Research Design; D018401:Sample Size; D012907:Smoking; D014675:Vegetables
D004043:Dietary Fiber; D001241:Aspirin