Chemoprevention is the attempt to prevent cancer from developing by using substances that interfere in the process of carcinogenesis.
Clinical trials are currently investigating chemoprevention for people at high risk of certain cancers. For instance, to prevent breast cancer in the second breast of women who have already been treated for breast cancer, or women who have never had breast cancer but are determined to be at high risk; or to prevent colon cancer in people with a genetic predisposition for that cancer. Individuals not at a particularly high risk can use behavioral and dietary modifications for chemoprevention. Since the 1980s, the National Cancer Institute has identified more than 1, 000 natural and synthetic chemicals with some degree of cancer preventive activity. Currently, over 400 potential agents are under investigation for their ability to prevent cancer and at least 40 compounds or combinations are undergoing human clinical trials.
Chemopreventive agents have been identified that interact with all stages of carcinogenesis; initiation, promotion and progression. They work by inactivating carcinogens (cancer-causing agents), inducing enzymes, or as antioxidants. Later in the process they may inhibit tumor growth by acting as suppressors or stimulating apoptosis.
Chemoprevention differs from chemotherapy in that it is used long before cancer develops to prevent cancer or to inhibit pre-cancer, possibly in at-risk individuals. Chemotherapy on the other hand seeks to kill cells that have already become cancerous. Chemoprevention uses natural products from foods or synthetic preparations. Because chemoprevention is used long-term, it must be non-toxic, effective, easy to administer and inexpensive. Few specific agents are currently advised for widespread clinical use since clinical trials that last up to 15 years are still ongoing.
Dietary factors and lifestyle changes are important areas in chemoprevention. It is estimated that through dietary improvements there could be a 50% reduction in colon and rectal cancers, 25% reduction in breast cancer and a 15% reductions each in prostate, endometrial and gallbladder cancers. Cancers of the stomach, esophagus, pancreas, ovaries, liver, lung and bladder may also be affected by dietary factors. Agents of importance in chemo-prevention include vitamins A, C and E as well as non-nutrient compounds from plants called phytochemicals.
Phytochemicals from food are a source of many chemopreventive agents. Garlic alone contains 30 cancer preventing compounds including selenium. Broccoli contains indole-3-carbinol as well as phenethylisothiocyanate, a sulfur-containing compound. Soy products contain phytoestrogens such as genistein. Tea, both black and green, contains an abundance of polyphenols such as the catechins that have antioxidant and anti-cancer activity. Compounds in tea also have anti-estrogen activity and can modulate detoxification enzymes. Curcumin from the spice turmeric is gaining attention as a chemopreventive agent. It is both an anti-inflammatory agent and an antioxidant. In laboratory animals curcumin has shown inhibition towards colon, breast, and stomach cancer.
Cindy L. A. Jones Ph.D., The Gale Group Inc., Gale, Detroit,