Many people are familiar with the blood thinning properties of warfarin, a drug that's widely taken to prevent heart attack and stroke. But now a new benefit has been discovered – that warfarin may also guard against cancer.
Warfarin is an inexpensive blood thinner. It's typically prescribed for patients whose leg arteries are prone to clots and for patients with the abnormal heartbeat called atrial fibrillation.
Now, Norwegian investigators say it may also protect against any type of cancer, but particularly against prostate, lung and breast cancer.
Lower colon cancer risk was also reported, but only in people taking warfarin for A-fib, according to the study.
The report was published online in the journal JAMA Internal Medicine.
The findings don't prove that warfarin reduces the risk of cancer, cautioned lead researcher James Lorens.
"This is an observational study using data on more than 1.25 million people 50 and older from Norwegian national registries, and cannot prove a cause-and-effect relationship," said Lorens, a professor of biomedicine at the University of Bergen in Norway.
Among adults taking warfarin, however, fewer developed cancer compared with those not taking the drug, Lorens said.
This study suggests there is something about warfarin that might reduce the risk of cancer, said Dr Len Lichtenfeld, deputy chief medical officer at the American Cancer Society.
Frequent blood tests needed
However, "the study does not suggest that we should be prescribing warfarin to reduce cancer risk," he said. "No one should be taking warfarin as a cancer prevention measure."
Lichtenfeld added that a healthy diet and exercise are better ways to prevent cancer than taking warfarin.
Experimental cancer models have found that warfarin blocks a receptor called AXL on tumour cells, which might explain why it could prevent cancers, he said.
As many as 10% of adults in Western countries take warfarin, according to background notes with the study. As a blood thinner, warfarin works by blocking vitamin K, which is essential for clotting. But the drug is difficult to regulate, and frequent blood tests are needed to ensure the dose is high enough to prevent clotting, but not so high as to cause major bleeding.
New drugs that don't need such careful monitoring, such as Xarelto (rivaroxaban) and Eliquis (apixaban), have started to replace warfarin.
Different mechanism of action
However, according to a previous Health24 article, these newer drugs are more expensive, so it's likely that warfarin will continue to be the most widely used drug for patients with atrial fibrillation
Because these new drugs have a different mechanism of action, "we do not expect the same cancer protective effect as warfarin," Lorens noted.
Rolf Brekken is a professor of surgery at the Center for Therapeutic Oncology Research at the University of Texas Southwestern Medical Center in Dallas. He hopes to see a trial testing warfarin in patients who have had cancer.
"The next step is to demonstrate that a low dose of warfarin is safe and effective in preventing a return of cancer," he said.
For the latest study, Lorens and his colleagues collected data on warfarin use and cancer among Norwegians born between 1924 and 1954.
Study has limitations
Specifically, the researchers looked at prescriptions for warfarin between 2004 and 2012 and any new cases of prostate, lung, breast and colon cancer between 2006 and 2012.
Among 1.25 million people, nearly 93 000 were taking warfarin.
Warfarin's anti-cancer effect was particularly strong among patients taking it for atrial fibrillation, Lorens said.
The study had some limitations. Because Lorens' team did not collect information on other medications or risk factors, "new" cancers may have been recurrences of previous ones.
Also, warfarin prescriptions may be a marker for other factors that can help prevent cancer, they added.