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An Overview of Clinical Cancer Chemoprevention Studies with Emphasis on Positive Phase III Studies¹

David S. Alberts^2,*,, and Dava J. Garcia

^* Department of Medicine, Section of Hematology and Oncology Arizona Cancer Center, College of Medicine, University of Arizona, Tucson, AZ 85724

Cancer prevention aims to halt or reverse the development and progression of precancerous cells through the use of noncytotoxic nutrients and/or pharmacologic agents during the lengthy time period between tumor initiation and frank malignancy. This paper reviews cancer chemoprevention studies and focuses on Phase III trials, which are large, randomized, placebo-controlled studies that usually last several years. Studies may include multiple agents and dose levels, long-term toxicity evaluations or the modulation of surrogate endpoint biomarkers. Sample sizes of individual studies vary depending on statistical concerns and the demographics of the subject population. Recent Phase III trials include several promising agents: retinol; the retinoids 13-cis retinoic acid, all-trans-retinoic acid and 4-hydroxyphenyl retinamide; ß-carotene; finasteride and tamoxifen. Because one of the many actions of retinoids is the induction of epidermal differentiation, clinical trials with this class of agents have largely been conducted in epithelial or squamous cell tumor types. Several Phase III studies that have targeted the reversal of premalignant lesions or the prevention of second primary tumors have shown promising positive results. In contrast, some studies have shown that chemopreventive agents may have limited activity against the recurrence or progression of cells that have already undergone malignant transformation. Thus, the role of chemoprevention appears to lie in reversal of the premalignant process rather than suppression of malignant growth.

KEY WORDS: • cancer prevention • chemoprevention • clinical studies • preneoplasia

¹ Presented at the First International Symposium on the Role of Soy in Preventing and Treating Chronic Disease, held in Mesa, AZ, February 20–23, 1994. The symposium was sponsored by Protein Technologies International, the soybean growers from Nebraska, Indiana and Iowa and the United Soybean Board. Guest editors for this symposium were Mark Messina, 1543 Lincoln Street, Port Townsend, WA 98368, and John W. Erdman, Jr., Division of Nutritional Sciences, University of Illinois, Urbana, IL 61801-3852.

² To whom correspondence should be addressed: Arizona Cancer Center, 1515 N. Campbell Avenue, Tucson, AZ 85724.