According to the results of a study published in Lancet Oncology, men who had used the blood thinner warfarin for four years were 20% less likely to develop prostate cancer than men who had never used warfarin.

Warfarin is an anticoagulant medication that is used to prevent blood clots. Although there is some suggestion that warfarin may reduce the risk of certain types of cancer, results of previous studies have been mixed.

To explore the relationship between warfarin and risk of urogenital cancer, researchers in Canada conducted a study among more than 19,000 individuals with cancer of the prostate, urinary bladder, kidney, ovary, or uterus, and a comparison group of more than 116,000 individuals without cancer.

• Warfarin use did not influence the risk of bladder cancer, kidney cancer, ovarian cancer, or uterine cancer.
• Men who had used warfarin for four out of five of the preceding years (the most recent year was not considered in the analysis) were 20% less likely to develop prostate cancer than men who had never used warfarin.

The researchers conclude that warfarin may have an anticancer effect that reduces the risk of prostate cancer. This result will need to be confirmed by other studies, however. In addition to a direct effect of warfarin, there are several other possible explanations for the lower risk of prostate cancer in warfarin users. For example, the reduced risk of prostate cancer may result from the health conditions that prompt warfarin use, rather than from the warfarin itself.

Because warfarin carries a risk of bleeding complications, is it unlikely to have broad applicability for cancer prevention even if the protective effect on prostate cancer is confirmed. However, if warfarin proves to reduce the risk of prostate cancer, an understanding of the basis for this effect may guide the development of new approaches to prostate cancer prevention or treatment.

Reference: Tagalakis V, Tamim H, Blostein M, Collet J-P, Hanley JA, Kahn SP. Use of warfarin and risk of urogenital cancer: a population-based, nested case-control study. Lancet Oncology. 2007;8:395-402.