After nearly 20 years of tantalizing hints that vitamins or other food substances might prevent cancer, researchers say they have finally proved that this strategy works.
By giving people a form of a vitamin, they prevented one type of cancer.
In a study being published today, researchers at the M. D. Anderson Cancer Center of the University of Texas in Houston report that high doses of a derivative of vitamin A, marketed as the acne drug Accutane, 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.
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 thus are at relatively high risk to get head or neck cancers.
And the finding strongly indicates that other cancers might also be preventable.
Cancer specialists envision the start of a new era in which they cutthe cancer toll by identifying people who are at high risk because of their genes or their habits, like 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.
Dr. Peter Greenwald, director of cancer prevention and control at the National Cancer Institute in Bethesda, said the new study "is tremendously important and tremendously exciting."
In the study, 50 patients who had already had a tumor in the head or neck removed by chemotherapy or surgery took the drug isotretinoin, marketed as Accutane, for a year and were monitored for another 32 months.
Only two, or 4 percent, of them developed another cancer.
In contrast, 12 of 50 patients who took a dummy pill for comparison, or 24 percent, developed a new cancer during the study.
In head and neck cancer, although nearly every person who is treated in the early stages of the diseases will be cured of that cancer, about one-third of the patients will go on to develop a second cancer of the head, neck, or lungs that is unrelated to the first cancer.
Until now, cancer researchers have had only indirect evidence that dietary components can prevent cancer.
For example, they have compared populations of different countries and noticed that people who eat a lot of fruit and vegetables and less fat have fewer cancers than those who eat more fat and less vegetables.