Warfarin use is associated with a lower risk of cancer, according to results from a large, population-based study of persons older than 50 years published in JAMA Internal Medicine.
The research team, led by Gry S. Haaland, MD, from the Department of Biomedicine at the University of Bergen in Norway, conducted a nationwide cohort study using the Norwegian National Registry to examine the association between warfarin use and cancer incidence. Data were collected from January 1, 2004, to December 31, 2012, and analysis was conducted from October 15, 2016, to January 31, 2017.
The study cohort (n = 1,256,725) included all persons born between January 1, 1924, and December 31, 1954, who were living in Norway from January 1, 2006, through December 31, 2012. The cohort was coupled with the Cancer Registry of Norway (CRN) to retrieve information on all cancers diagnosed between January 1, 2006, and December 31, 2012, and with the Norwegian Prescription Database (NorPD) to retrieve information on warfarin prescriptions filled from January 1, 2004, through December 31, 2012.
The study was divided into 2 groups: warfarin users and nonusers. Warfarin users received a warfarin prescription at least 2 years before any cancer diagnosis and had an interval between first and last prescription of at least 6 months. For warfarin users without a cancer diagnosis, the interval between first and last prescription had to be at least 6 months.
From the cohort, 607,350 (48.3%) were male, 649,375 (51.7%) were female, 132,687 (10.6%) had cancer, 92,942 (7.4%) were classified as warfarin users, and 1,163,783 (92.6%) were classified as nonusers. Warfarin users were older, with a mean age of 70.2 years, and were predominantly men (57,370 [61.7%]), compared with nonusers, who had a mean age of 63.9 years and were mostly women (613,803 [52.7%]). Warfarin users had a significantly lower age- and sex-adjusted incidence rate ratio (IRR) in all cancer sites (IRR, 0.84) and in prevalent organ-specific sites: lung, 0.80; prostate, 0.69; and breast, 0.90. No significant effect was observed in colon cancer (0.99).
In a subgroup analysis of patients with atrial fibrillation or atrial flutter, the IRR was lower in all cancer sites (IRR, 0.62) and in prevalent sites: lung, 0.39; prostate, 0.60; breast, 0.72; and colon, 0.71.
“Our data indicate that warfarin provides a possible cancer protection, a finding that may have important implications for choosing medications for patients who need anticoagulation,” the authors stated. “Further studies are warranted to fully elucidate the mechanisms underpinning these observations.”
Haaland GS, Falk RS, Straume O, Lorens JB. Association of warfarin use with lower overall cancer incidence among patients older than 50 years. JAMA Intern Med. 6 November 2017. doi:10.1001/jamainternmed.2017.5512