Warfarin may lower incidence of breast cancer in older adults

Robyn Boyle, RPh, for MDLinx | December 01, 2017

Warfarin may decrease the risk of some types of cancers—including breast cancer—in people older than 50 years of age, according to a study published in JAMA Internal Medicine.

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While the antitumor potential of warfarin has been demonstrated in cancer model systems, previous clinical studies that have examined the association between warfarin and cancer risk have yielded mixed results.

“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,” wrote the team of researchers lead by Gry S. Haaland, MD, at the University of Bergen, Norway.

While the antitumor potential of warfarin has been demonstrated in cancer model systems, previous clinical studies that have examined the association between warfarin and cancer risk have yielded mixed results.

The large population-based cohort study used the Norwegian National Registry along with the Norwegian Prescription Database (NorPD) and the Cancer Registry of Norway (CRN). The Norwegian National Registry includes health information about every person in Norway, and the CRN collects information about all cancer occurrences in the country. The NorPD collects data on all drugs dispensed in pharmacies, but not in hospitals.

The cohort was all people born between January 1924 and December 1954. It was divided into warfarin users and nonusers; a subgroup of people taking warfarin for atrial fibrillation or atrial flutter was also identified.

Dr Haaland and colleagues applied a strict definition of warfarin use, with a 2-year minimum time interval between start of warfarin treatment and cancer diagnosis.

Of the 1,256,725 people in the cohort, 10.6% had cancer and 7.4% were warfarin users. There was a significantly lower age- and gender-adjusted incidence rate ratio (IRR) in all cancer sites among warfarin users compared to nonusers. This was also true for lung, prostate, and breast cancers; but there was no significant effect in colon cancer.

In the subgroup of people with atrial fibrillation or atrial flutter, the IRR was lower in all cancer sites, as well as in organ-specific sites: lung, prostate, breast, and colon, indicating that warfarin use may have a protective effect.

The authors acknowledged several limitations of the study. The NorPD lacks information on medications used in hospitals and nursing homes, and there was missing information regarding other medications used by patients that might contribute to the development of cancer. Cancer diagnoses prior to the study and information on lifestyle choices such as diet and smoking that may contribute to cancer were also not available.

“Further studies are warranted to fully elucidate the mechanisms underpinning these observations,” the authors concluded.

To read more about this study, click here

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