NEW ORLEANS -- In a case of medical serendipity, the cholesterol-lowering pills called statins, widely prescribed to prevent heart attacks, also appear to have an unintended but potentially substantial benefit of warding off cancer.
Statins are among the world's most commonly used medicines. Evidence has been building for several years that people who take them to improve their cholesterol levels appear to reduce their risk of getting cancer.
The latest data, released yesterday at a cancer conference, found that people who took statins for at least five years appeared to cut their risk of colon cancer in half. Earlier work has shown reductions in breast and prostate cancer as well as across-the-board cancer risk.
Specialists have other reasons to think the statins might be cancer fighters. Experiments involving lab animals and cells growing in test tubes suggest a possible role for statins.
For the most part, researchers say the evidence is still too weak to recommend taking statins alone for cancer prevention. They say those who take such pills for other reasons may be getting a bonus benefit.
The data so far ''fit with what we know from the lab," said Dr. Monica Morrow of Northwestern University.
''But we can't say this is enough proof for people to go out and take statins."
To be convinced, doctors say they would need to see a carefully controlled experiment designed specifically to show that statins reduce cancer risk. The data so far are based largely on watching what happens to people who take statins for reasons that have nothing to do with cancer.
The latest of these studies, directed by Dr. Stephen Gruber of the University of Michigan, was presented at this weekend's meeting of the American Society of Clinical Oncology.
His team, working in Israel, looked at 1,708 people who had colon cancer and 1,737 who did not. Those on statins for at least five years had about a 50 percent reduction in the risk of this malignancy.
Adjusting for other factors that could possibly explain the difference, such as better health habits, did not change the strong link between statins and lowered risk. Also, those who took other varieties of cholesterol drugs had no cancer protection.
''I think these data are very exciting and potentially good news for future studies that will allow us to come up with clinical recommendations," Gruber said.
Specialists have been misled by such data in the past. For instance, based on similar studies, doctors long believed that taking estrogen supplements after menopause would lower women's risk of heart attacks. A careful experiment proved this wrong, and it is still unclear why the estrogen users seemed to have less risk.
If statins do lower the risk of cancer, scientists say, it may have nothing to do with their effect on cholesterol. One theory is that statins could ward off the disease by lowering inflammation. Another is that their primary job, reducing an enzyme called HMG CoA, could block the working of some cancer-causing genes.
One concern about suggesting statins to prevent cancer without definitive proof of their worth is the risk of exposing people to possible side effects, even when the risk is small. Statins can cause muscle and liver problems.
''The consensus is, yes, this agent does have the ability to reduce the incidence of breast cancer, but the risk of blood clots needs to be kept in mind," said the study's director, Dr. Silvana Martino of the Cancer Institute Medical Group in Santa Monica, Calif.
Statins are hardly the first drugs with possible unanticipated benefits. Aspirin, once just a painkiller, is now a mainstay of preventing and treating heart attacks, and some evidence suggests it, too, can lower the risk of colon cancer.
The bone-strengthening drug Evista, or raloxifene, appears to substantially lower the risk of breast cancer in older women who are at relatively low risk of the disease. New long-term follow-up data, presented at the conference, showed a 66 percent reduction after eight years of use for osteoporosis.