The effect of warfarin on the risk of prostate cancer

Abstract

14524 Background: The anticancer activity of oral anticoagulants has been a matter of debate for several years. Recent evidence suggests that prolonged treatment with warfarin may be associated with a reduced incidence of newly diagnosed urogenital cancer during long-term follow-up of patients with venous thromboembolism. The aim of this study was to assess whether exposure to warfarin was associated with reduced risk of prostate cancer in a large population-based cohort. Methods: We conducted a matched case-control study nested within the population of beneficiaries of the Saskatchewan Prescription Drug Plan aged 50 years and older from 1981–2002 with no history of cancer since 1967. New cases of prostate cancer diagnosed between 1981 and 2002 were identified using the linked Saskatchewan Cancer Agency registry. Six controls per case matched on age, gender, and sampling time were randomly selected. The cumulative exposure to warfarin in the five years preceding the cancer diagnosis was assessed. Prescription counts were used to define warfarin exposure. Exposure in the year immediately preceding the cancer diagnosis was excluded to control for detection bias. Conditional logistic regression analysis was used to assess confounding by other drugs such as nonsteroidal anti-inflammatory medications. Results: Among 11502 cases and 69012 controls, 7.4% of cases and 7.1% of controls had a history of any warfarin use. Compared to men who had never used warfarin, adjusted odds ratio (OR) for prostate cancer among ever-users in the 5 year period was 0.94 (95% confidence interval (CI), 0.86–1.03). In those who accumulated 1, 2, 3 and 4 years of warfarin use, the adjusted ORs were 1.01 (95% CI, 0.89–1.16), 1.00 (95% CI, 0.82–1.23), 0.81 (95% CI, 0.60–1.09), and 0.80 (95% CI, 0.65–0.99), respectively (p-trend=0.03). Conclusion: Our results suggest that cumulative use of warfarin of at least 4 years may be associated with a reduced risk of prostate cancer. However, confounding by other determinants of prostate cancer associated with warfarin use is possible. Nonetheless, confirmation of these findings by prospective studies may provide the evidence necessary to consider the use of warfarin in prostate cancer prevention. No significant financial relationships to disclose.