Warfarin Linked to Lower Cancer Risk

Use of the blood thinner warfarin (Coumadin, Bristol-Myers Squibb) has been linked to a reduced incidence of cancer in a large population-based cohort study. Losing this possible protection against cancer may be a consequence of switching patients from warfarin to newer anticoagulant drugs.

In the study, published in JAMA Internal Medicine, Norwegian researchers set out to discover whether warfarin, prescribed to as many as 10% of adults in Western countries, is associated with an increased risk of cancer. They found that the use of warfarin was associated with a lower incidence rate ratio (IRR) for any cancer (0.84%) and, specifically, of three of the most common cancers: prostate (IRR 0.69), lung (IRR 0.80), and female breast cancer (IRR 0.90), compared to not using warfarin. There was no observed significant effect in colon cancer.

“An unintended consequence of this switch to new oral anticoagulants may be an increased incidence of cancer, which is an important consideration for public health,” wrote James B. Lorens, PhD, a co-author of the study and Professor in the Department of Biomedicine at the University of Bergen in Norway.

Lorens and colleagues used data from the Norwegian National Registry on 1.25 million people born in Norway between 1924 and 1954. They divided the cohort into those taking warfarin (92,942) and those not taking warfarin (more than 1.1 million).

Individuals taking warfarin for atrial fibrillation or atrial flutter were studied as a subgroup. In the subgroup of people using warfarin for atrial fibrillation or atrial flutter, the risk for cancer at any site was lower and was also lower in all four common sites (lung, prostate, breast, and colon).

"These results indicate that a compound used by millions of patients may be associated with a reduced cancer risk. This can give new insight into cancer prevention and is important to follow up,” Lorens said, in an article published by the University of Bergen.

"When we started this study, we certainly had a hypothesis that there may be a connection between warfarin use and cancer prevalence, but that the effect would include so many types of cancer, and that it would be so big for some cancer types, that surprised us,” said coauthor Oddbjorn Straume, D, PhD, a physician in the Department of Oncology at Haukeland University Hospital in Bergen, quoted in the university article.

However, observational findings are not enough to allow researchers to draw conclusions about whether it is warfarin or other factors that caused the reduction in cancer, the researchers noted.

"To be sure to what extent warfarin can be used to prevent cancer, we need to perform a prospective clinical intervention study. Based on the results that we present now, we cannot recommend the use of warfarin besides its approved indication, yet,” Straume said.