Can Certain Drugs and Nutrients Prevent Cancer?

June 23, 2000 -- 'Chemoprevention,' the use of drugs and nutrients to prevent cancers, has become a buzzword among those involved in cancer research and treatment.

But although many studies of this method are under way, the results so far have been mixed. Some success have been seen with breast and bowel cancers, but lung cancer is a much tougher nut to crack, Gilbert Omenn, MD, PhD, writes in an editorial in the current issue of the Journal of the National Cancer Institute.

"Chemoprevention is the process of trying to reverse, suppress, prevent or delay the progression from a precancerous state to frank cancer," says Fadlo Khuri, MD, who commented on the method for WebMD. "We are currently using several different agents, both alone and in combination, for chemoprevention of new, first time cancers, called primary prevention, as well as second cancers in people who already have the disease, called secondary prevention." Khuri is chair of the radiation oncology group chemoprevention committee at M.D. Anderson Cancer Center in Houston.

One of the most difficult cancers to treat is lung cancer, and several studies using vitamin A-like molecules called retinoids for chemoprevention of this type of cancer have been completed or are going on now.

"Lung cancer is a formidable foe," Omenn, executive vice president for medical affairs at the University of Michigan in Ann Arbor, writes in the editorial. "It is the leading cause of deaths due to cancer in both women and men. Treatment results are very disappointing in the majority of patients. ... Chemoprevention has yet to succeed, either in primary prevention or in secondary prevention in patients with [lung and digestive tract] cancers."

Yet Omenn calls retinoids "among the most promising class of chemopreventive agents." Trials using retinoids, both alone and in combination with vitamin E (alpha-tocopherol) and other molecules are being conducted for skin cancer, lung cancer, cervical cancer, prostate cancer, and brain cancer.

Roberto Pili, MD, an instructor in oncology at Johns Hopkins University School of Medicine in Baltimore, tells WebMD that some combinations may work better than any single agent alone. "Our studies show an additive effect when the retinoid is used with another drug," he says. "We are also considering using these drugs in combination with traditional chemotherapeutic agents.

Should people who are interested in reducing their risk of cancer take vitamin A, vitamin E, or beta-carotene (another form of vitamin A) as supplements? "There are no long-term studies demonstrating the benefit of these vitamins for primary chemoprevention, Pili says, "but there is evidence they may be effective in secondary prevention. It's too early for anyone to say whether we should all be taking supplements, but I think we'll get there."

But there are some known ways to protect yourself, according to Omenn.

"The most reliable methods of reducing the incidence of cancers depend on avoidance of known carcinogenic agents, including radiation, tobacco, alcohol, various infectious agents, medical exposures to certain pharmaceuticals and hormones, ionizing radiation, and environmental and occupational exposures to a moderately long list of chemicals," he writes.

• Chemoprevention is a new branch of cancer research in which scientists look for ways to use drugs or nutrients to reverse, prevent, or delay the development of cancer. Researchers are testing molecules like vitamins A and E, as well as other chemicals and combinations.
• Preliminary studies seem to show vitamin supplementation can be helpful in preventing some second cancers in patients who already have the disease. More study is needed to confirm these findings.
• For now, the researchers say the best way known to fight cancer is to avoid things that cause it, like too much sun exposure and tobacco, as well as some medical products, chemical or radiation exposure, and certain types of infections.