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An off-target effect of the anticoagulant warfarin is inhibition of GAS6-AXL signaling, which enhances antitumor immunity. Also, animal and epidemiologic studies suggest that the use of warfarin might reduce cancer incidence.
To further examine the association between warfarin use and cancer incidence, investigators conducted a population-based cohort study of more than 1.2 million persons (age, >50 years) in the Norwegian national, cancer, and prescription registries. Participants were defined as warfarin users if they took the drug for at least 6 months and at least 2 years before being diagnosed with cancer.
Significantly fewer warfarin users than nonusers received a cancer diagnosis (9.4% vs. 10.6%; incidence rate ratio, 0.84; 95% confidence interval, 0.82–0.86), including significantly lower IRRs for prostate (0.69), lung (0.80), and breast cancer (0.90), but not colon cancer (0.99). To exclude patients that might have received warfarin for thromboembolic disease associated with occult malignancy, investigators analyzed a subgroup of patients whose indication for warfarin was atrial fibrillation or flutter. Their IRRs were lower than those of nonusers for all cancer sites (0.62), including prostate (0.60), lung (0.39), and breast cancer (0.72).
Haaland GS et al. Association of warfarin use with lower overall cancer incidence among patients older than 50 years. JAMA Intern Med 2017 Nov 6; [e-pub]. (http://dx.doi.org/10.1001/jamainternmed.2017.5512)
Comment
This large observational study shows a reduction in cancer incidence among regular warfarin users, but population-based studies cannot establish cause and effect. People on long-term warfarin therapy might differ in important respects from nonusers. For example, they modify their diets, avoid alcohol and various drugs, and often alter their lifestyles. Despite these limitations, the results of this study provide further support for the hypothesis that warfarin use decreases cancer incidence and warrants continued investigation.