Warfarin linked to lower rate of cancer, particularly for atrial fibrillation patients

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A recent study by Gry Haaland (University of Bergen, Bergen, Norway) et al published in the Journal of the American Association of Medicine (JAMA): Internal Medicine points to a possible association between warfarin use among patients older than 50 years and lower overall cancer incidence. The rates of cancer was further reduced for patients with atrial fibrillation (AF) or atrial flutter.

Warfarin use is prevalent in adult populations of Western countries, approximated by JAMA to be prescribed to as many as 10% of adults. Previous studies have investigated the hypothesis that the anticoagulant has cancer preventative effects, including Amanda Kirane (University of Texas Southwestern Medical Center, Dallas, USA) et al’s 2015 study on low doses of warfarin to block the progression and spread of pancreatic cancer, published in Cancer Research.

In the latest new research on the possible link between the oral anticoagulant and cancer prevention, Haaland et al have demonstrated significantly lower age- and sex-adjusted incidence rate ratio (IRR) of 0.84 in all cancer sites (95% CI, 0.82-0.86). In a subgroup analysis of patients with AF or atrial flutter, however, cancer rates decreased even further in all cancer sites (IRR, 0.62; 95% CI, 0.59-0.65) as well as in lung cancer (IRR, 0.39; 95% CI, 0.33- 0.46), prostate cancer (IRR, 0.60; 95% CI, 0.55-0.66), breast cancer (IRR, 0.72; 95% CI, 0.59-0.87) and colon cancer (IRR, 0.71; 95% CI, 0.63-0.81).

The data resulted from a population based cohort study using the Norwegian National Registry, the Norwegian Prescription Database and the Cancer Registry of Norway–a cohort of 1,256,725 participants born in 1924-1954 and living in Norway in the years 2006-2012. Haaland et al defined warfarin use as taking the prescription for a minimum of six months, with at least two years from first prescription to any cancer diagnosis. The subgroup, consisting of patients prescribed with warfarin for atrial fibrillation or flutter, included 33,313 patients. Haaland and co-investigator Jim Lorens (University of Bergen, Bergen, Norway) spoke to Cardiac Rhythm News about the subgroup analysis:

Thromboembolic disease, such as venous thromboembolism and pulmonary embolism, are associated with an elevated cancer risk. This is thought to be related to pro-coagulative circulating cancer cells from an undiagnosed malignancy. This was an important confounding factor in our study. To address this, we selected the patients in the cohort with atrial fibrillation or flutter. This group of patients lacks the occult pre-existing malignancy risk of thromboembolic patients, as they have no previous thrombosis in their medical history, but rather receive warfarin as a prophylactic treatment.”

Warfarin’s vitamin K antagonism is believed to be the property that may prevent or hinder the progression of cancer. Published at a time when a generation of non-vitamin K antagonising novel oral anticoagulants (NOACs) are increasingly favoured over warfarin due to improved safety and efficacy, the study investigators believe their findings “could have important implications for the selection of medication for patients needing anticoagulation.”

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