This article is more than 5 years old. Information may no longer be current.

Warfarin lowers cancer risk in older adults

Warfarin use was associated with a significantly lower rate of cancer incidence across a broad range of malignancies among adults over the age of 50 years, compared with nonuse, according to new research published in JAMA Internal Medicine.

“Warfarin sodium is the most used anticoagulant worldwide and is prescribed to 5% to 10% of the adult population in Western countries ... Previous epidemiological studies differ regarding the association between warfarin and cancer, with one suggesting a specific association with urogenital cancers and another indicating no association with cancer incidence,” Gry S. Haaland, MD, from the department of biomedicine at the University of Bergen, Norway, and colleagues wrote.

Newer nonwarfarin anticoagulants have become increasingly available; therefore, it is important to clearly determine any association between warfarin and cancer, according to the researchers. Thus, Haaland and colleagues conducted a population-based cohort study to investigate whether warfarin use is related to cancer incidence.

The researchers used the Norwegian National Registry to identify all individuals born between Jan. 1, 1924, and Dec. 31, 1954 who were residents of Norway between Jan. 1, 2006, and Dec. 31, 2012 (n = 1,256,725; 48.3% male; 10.6% had cancer). They also used the Norwegian Prescription Database and the Cancer Registry of Norway to examine warfarin prescriptions and cancer diagnoses among the study population, respectively.

Patients were categorized as warfarin users (7.4%) or nonusers (92.6%). Warfarin users included those who were prescribed warfarin at least 2 years before a cancer diagnosis and used the drug for at least 6 months.

The researchers created a subgroup consisting of those prescribed warfarin for atrial fibrillation or atrial flutter.

Warfarin users had a mean age of 70.2 years and were mostly men (61.7%), while nonusers had a mean age of 63.9 years and were mostly women (52.7%).

Compared with nonusers, warfarin users had a significantly lower age- and sex-adjusted incidence rate ratio (IRR) for all cancer types (IRR = 0.84;95% CI, 0.82-0.86) and common organ-specific cancers, including lung (IRR = 0.8; 95% CI, 0.75-0.86), prostate (IRR = 0.69; 95% CI, 0.65-0.72) and breast (IRR = 0.9; 95% CI, 0.93-1.06), but not colon (IRR = 0.99; 95% CI, 0.93-1.06).

The subgroup analysis revealed that warfarin users with atrial fibrillation or atrial flutter had a significantly lower IRR in all cancer sites (IRR = 0.62; 95% CI, 0.59-0.65) and the most common cancer sites, including lung (IRR = 0.39; 95% CI, 0.33-0.46), prostate (IRR = 0.60; 95% CI, 0.55-0.66), breast (IRR = 0.72; 95% CI, 0.59-0.87) and colon (IRR = 0.71; 95% CI, 0.63-0.81), compared with nonusers.

“Our results document a lower incidence of cancer associated with warfarin in a population-level study,” Haaland and colleagues concluded. “We observed a lower relative risk in a large cohort comprising many different cancer types, reinforced by a subgroup analysis of patients with [atrial fibrillation or atrial flutter] who were receiving warfarin treatment to prevent thromboembolic events.”

They added, “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. Further studies are warranted to fully elucidate the mechanisms underpinning these observations.” – by Alaina Tedesco

Disclosure: Haaland reports no relevant financial disclosures. Please see study for list of all other authors’ relevant financial disclosures.