As Clinical Studies Mature, Dietary Factors that Prevent Colon Cancer May Be Defined

With the maturation of several clinical trials in the late 1990s,oncology researchers are on the verge of determining which typesof nutritional interventions will be effective in the primaryprevention of colon cancer, David S. Alberts, md, said at theNational Conference on Colorectal Cancer, sponsored by the AmericanCancer Society.

The use of dietary elements to prevent colon cancer has had aspotty record in recent clinical trials. No intervention effectfrom the antioxidants beta-carotene and vitamins C and E was demonstratedat colonoscopy after 1 year in a study of 864 patients reportedby Dr. Robert Greenberg of Dartmouth University in 1994.

However, a diet high in unrefined wheat bran fiber and low infat prevented the recurrence of polyps larger than 10 mm overa period of 4 years in a randomized blinded study of 424 patients,presented by Dr. Finlay Macrae of the Royal Melbourne Hospitalin May 1995.

"This is the first study showing a positive association betweennutritional interventions and sporadic colon polyp preventiondone with a randomized blinded design that we can build upon,"said Dr. Alberts, director, Prevention & Control, ArizonaCancer Center, Tucson.

Dr. Alberts observed that four major clinical trials of nutritionalinterventions will provide clues concerning the importance oflowering the amount of dietary fat and increasing the consumptionof fruits and vegetables, wheat bran, calcium carbonate, and selenium.

NCI Intervention Study

The Nutritional Intervention Study, under the direction of Dr.Arthur Schatzkin, of Memorial Sloan-Kettering Cancer Center, isbeing conducted through the National Cancer Institute at eightseparate sites. The study includes 2,000 post-polypectomy patientswho have been randomized to follow either a diet low in fat (lessthan 20% of daily calories from fat) and high in fruits and vegetables(five to eight servings a day) or the standard American diet.

The average patient in the intervention arm of the study is consumingapproximately 25% of daily calories from fat and six servingsof fruits and vegetables each day, Dr. Moshe Shike said at theconference. This contrasts with the usual American diet, whichconsists of 35% of calories from fat and only two to three dailyservings of fruits and vegetables.

The objective of the Nutritional Intervention Study is to examinethe interaction of fruits and vegetables and a low-fat diet, notthe effect of a single dietary component, on the recurrence ofcolorectal polyps at colonoscopy. The study has accrued all ofits subjects and will conclude in 1998 or 1999, Dr. Shike said.

Another dietary intervention study, from the University of Arizona,is following 1,429 patients from the Phoenix metropolitan areawho had an initial index polyp resected. The patients are beingrandomized to receive wheat bran in the form of cereal or breakfastsnack bars, either 2 or 13.5 g/d, for up to 5 years. The end pointof the study will be the results of colonoscopy between 3 and4 years.

Effects of Calcium and Selenium

A multicenter study of the effect on polyp recurrence of consuming1,200 mg/d of calcium carbonate for 3 years has been completedand is under analysis. The study is being coordinated by Dr. JohnBaron of Dartmouth University, and includes 900 patients who haveundergone resection for adenomatous polyps.

A recently completed multicenter study of selenium in skin cancerpatients also may have a bearing on colon cancer, Dr. Albertssaid. Under the direction of Dr. Larry Clark of the Universityof Arizona, the study evaluated the use of 200 or 400 mcg of seleniumin 1,700 individuals with skin cancer that had been resected.The preliminary analysis of the results of the intervention hasbeen completed, and a paper has been submitted for publication.