James B. Lorens, PhD
A Norwegian population–based cohort study indicated that the use of warfarin was associated with a reduced risk of cancer overall and site-specific cancers among patients aged > 50 years. The findings were reported in JAMA Internal Medicine by Haaland et al. As noted by the investigators, studies in cancer models have shown that warfarin inhibits AXL receptor tyrosine kinase–dependent tumorigenesis and increases antitumor immune responses at doses below anticoagulation levels. James B. Lorens, PhD, of the University of Bergen, Norway, is the corresponding author of the JAMA Internal Medicine article.
The study involved data from the linked Norwegian National Registry, Norwegian Prescription Database, and Cancer Registry of Norway. The study cohort included 1,256,725 persons born between January 1924 and December 1954 who resided in Norway from January 2006 through December 2012. Warfarin use was defined as taking at least 6 months of a warfarin prescription and at least 2 years from the first prescription to any cancer diagnosis. A subgroup of users consisted of patients taking warfarin for atrial fibrillation or atrial flutter. Overall, 10.6% of the cohort had cancer, and 7.4% were warfarin users. The primary outcome measure was cancer diagnosis of any type during the 7-year observation period from January 2006 through December 2012.
The age- and sex-adjusted incidence rate ratio (IRR) for warfarin users vs nonusers was 0.84 (95% confidence interval [CI] = 0.82–0.86) for all cancer sites, 0.80 (95% CI = 0.75–0.86) for lung cancer, 0.69 (95% CI = 0.65–0.72) for prostate cancer, and 0.90 (95% CI = 0.82–1.00) for breast cancer, with no significant effect seen for colon cancer (IRR = 0.99, 95% CI = 0.93–1.06). In the subgroup of users with atrial fibrillation or atrial flutter (36% of the user group), the IRR was lower in all cancer sites (0.62, 95% CI = 0.59–0.65) and for lung cancer (0.39, 95% CI = 0.33–0.46), prostate cancer (0.60, 95% CI = 0.55–0.66), breast cancer (0.72, 95% CI = 0.59–0.87), and colon cancer (0.71, 95% CI = 0.63–0.81).
The investigators concluded: “Warfarin use may have broad anticancer potential in a large, population-based cohort of persons older than 50 years. This finding could have important implications for the selection of medications for patients needing anticoagulation.” ■