Researchers say they have proved that what you ingest may help prevent cancer.
Until now, cancer researchers have had only indirect evidence that dietary components can prevent the disease.
In a study being published today, researchers at the M.D. Anderson Cancer Center of the University of Texas in Houston report that by giving people a form of a vitamin, they prevented one type of cancer.
Dr. Peter Greenwald, director of cancer prevention and control at the National Cancer Institute in Bethesda, Md., said the new study "is tremendously important and tremendously exciting."
He said it was the first controlled study that shows such a result and "gives us the final proof" that the strategy known as chemoprevention of cancers works.
Cancer specialists envision the start of a new era in which they cut the cancer toll by identifying people who are at high risk because of their genes or their habits, such as smoking, and then intervene to prevent cancer by giving them vitamin derivatives or other drugs.
"This is a landmark study," said Dr. Frank L. Meyskens Jr., director of the Clinical Cancer Center at the University of California at Irvine.
"It gives a clear message that what we've seen in the test tube and in animals can work in humans." Meyskens said the finding "should galvanize the field."
The Houston team gave patients a high doses of a derivative of vitamin A, marketed as the acne drug Accutane, that seemed to prevent lung, throat and mouth cancers in people who are at high risk of developing them.
The patients had been successfully treated for one episode of head or neck cancer.
But because their tissues were already primed to become cancerous, they were highly likely to grow new, separate cancers that were more life-threatening than the first.
Accutane prevented these new cancers from forming in most patients in the study for nearly three years, the researchers reported.
The drug did not prevent the spread or recurrence of the original tumor.
Accutane has serious side effects at high doses, but experts say that if the researchers can show lower doses also work, the stage will be set for giving Accutane to people who smoke or drink heavily, and so are at relatively high risk to get head or neck cancers.
Dr. E. Robert Greenberg, a professor of community and family medicine at Dartmouth Medical School, said, "It is very encouraging that it looks like there's something beyond theoretical evidence that we might be able to prevent cancer."
Greenberg directed a second study being published today that found that another form of vitamin A, beta carotene, did not prevent skin cancers in patients at high risk of developing them.
But, Greenberg said, "the issue is still open" on whether beta carotene might prevent other types of cancers.