A new study adds to evidence that bone drugs may play a role in suppressing cancer development, although there is still no proof that taking the medications would stave off malignancies.
The drugs, called bisphosphonates, have generated both good and bad headlines recently. Some work has linked them to fewer cases of cancer, while other research has found an increased risk of certain thigh fractures and serious jaw problems among women who take the drugs to treat the bone-thinning disease osteoporosis.
In the new study, researchers found that women on Actonel were only half as likely to be diagnosed with colon cancer as those who'd gotten just one prescription for the drug or none at all.
"At this point, I think people who are already taking the drug can be reassured," Dr. Harminder Singh, who worked on the study, told Reuters Health.
But he added that it's too soon to think about taking Actonel to prevent cancer.
"For people to start taking it, there are a few other things that need to be worked out, the cost and the side effects," said Singh, of the University of Manitoba in Canada.
According to the American Cancer Society, one in 19 men develops colorectal cancer at some point, and slightly fewer women do. The disease is the third leading cause of cancer deaths in the U.S.
An Israeli study published earlier this year found a link between bisphosphonates and a lower risk of colon cancer among women, but it wasn't clear how to explain that result. It could be that the drugs have protective effects, or it could be that women taking them are healthier overall.
In contrast to the Israeli work, Singh's study, which is published in the journal Cancer, takes into account how often people see their doctors, one factor that might muddy any differences found between those who take bone drugs and those who don't.
The research team tapped into data from a cancer registry in Manitoba, comparing colon cancer patients to people without the disease, but of the same age and sex.
About 1.1 percent (264) of the nearly 25,000 women in the comparison group had been given Actonel by their doctor, while only 0.6 percent (15) of 2,493 women with colon cancer had gotten the drug.
One way to interpret those findings is to chalk the difference up to a protective effect of Actonel. Indeed, women on that medication had 45 percent lower odds of having colon cancer than those who didn't take it.
But with a study design where you only observe patients, you can't ever be certain why some fare better than others, Singh cautioned.
"The ultimate proof of these agents would be a randomized controlled trial," he explained.
What's more, the researchers didn't have enough data to see if the findings would hold up for men, and they didn't find any reliable effects for the other bone drugs.
Even if Actonel did afford some protection against tumors, it's not cheap and its long-term side effects are not well known. The U.S. Food and Drug Administration is currently reviewing evidence suggesting bone drugs might raise the risk of esophageal cancer.
A month's supply of Actonel generally costs over $100.
So far, quitting smoking is one of the only things that experts agree will lower the risk of cancer.
For colon cancer in particular, the U.S. Preventive Services Task Force, a federally supported expert panel, advises screening all people between 50 and 75 using stool tests, sigmoidoscopy or colonoscopy.