Haaland GS, et al. - Herein, the authors scrutinized the connection between warfarin use and cancer incidence. In a large, population-based cohort of individuals older than 50 years, warfarin use could display broad anticancer potential. This data possibly exhibited significant implications for the selection of medications, in the case of patients requiring anticoagulation.

Methods

• The Norwegian National Registry coupled with the Norwegian Prescription Database and the Cancer Registry of Norway were used for this research.
• It included individuals (N = 1,256,725) born between January 1, 1924, and December 31, 1954, residing in Norway from January 1, 2006, through December 31, 2012.
• They were allocated into 2 groups: Warfarin users and nonusers.
• Candidates taking warfarin for atrial fibrillation or atrial flutter belonged to the subgroup.
• Data extraction took place from January 1, 2004, to December 31, 2012.
• Data analysis was carried out from October 15, 2016 to January 31, 2017.
• As a part of the exposures, warfarin use was defined as taking at least 6 months of a prescription and at least 2 years from first prescription to any cancer diagnosis.
• If warfarin treatment started after January 1, 2006, each person contributed person-time in the nonuser group until the warfarin user criteria were fulfilled.
• Cancer diagnosis of any type during the 7-year observation period (January 1, 2006, through December 31, 2012) served as the main outcome measure.

Results

• A total of 607,350 (48.3%) enrollees 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 (SD) age of 70.2 (8.2) years, and were predominantly men (57 370 [61.7%]) as compared with nonusers, who had a mean (SD) age of 63.9 (8.6) years and were mostly women (613 803 [52.7%]).
• A considerably lower age- and sex-adjusted incidence rate ratio (IRR) was reported in all cancer sites (IRR, 0.84; 95% CI, 0.82-0.86) and in prevalent organ-specific sites (lung, 0.80 [95% CI, 0.75-0.86]; prostate, 0.69 [95% CI, 0.65-0.72]; and breast, 0.90 [95% CI, 0.82-1.00]), among warfarin users and compared with nonusers.
• No notable effect was yielded in colon cancer (IRR, 0.99; 95% CI, 0.93-1.06).
• The subgroup analysis of patients with atrial fibrillation or atrial flutter revealed that the IRR was lower in all cancer sites (IRR, 0.62; 95% CI, 0.59-0.65) and in prevalent sites (lung, 0.39 [95% CI, 0.33-0.46]; prostate, 0.60 [95% CI, 0.55-0.66]; breast, 0.72 [95% CI, 0.59-0.87]; and colon, 0.71 [95% CI, 0.63-0.81]).