Abstract
Objective: Anticoagulants, especially vitamin K antagonists (VKAs) such as warfarin, have been hypothesized to have antitumor properties, and use of VKAs has been associated with a lower prostate cancer (PCa) risk. This study estimated PCa risk among users of warfarin and other anticoagulants.
Materials and methods: All anticoagulant use among 78,615 men during 1995–2009 was analyzed. Cox regression, adjusted for age, screening trial arm and use of other medications, with medication use as a time-dependent variable, was used to estimate PCa risk overall, and by tumor grade and stage.
Results: In total, 6537 men were diagnosed with PCa during 1995–2009 (1210 among warfarin users). Compared to non-users, warfarin use was associated with an increased risk of PCa [multivariable-adjusted hazard ratio (HR) = 1.11, 95% confidence interval (CI) 1.01–1.22]. This was limited to short-term, low-dose use, and was not observed in long-term use. A similar overall risk increase was observed for Gleason grade 7–10 PCa. Low-dose, short-term use of warfarin was associated with an increased risk of metastatic PCa. However, the increase in risk vanished with continued use. Compared to other anticoagulants, low-dose use of warfarin was associated with a slightly elevated overall PCa risk (HR = 1.19, 95% CI 1.00–1.43). The increase in risk disappeared in long-term, high-dose use.
Conclusions: This study, which included a larger number of PCa cases with warfarin exposure than previous studies, does not support previous notions of decreased risk of PCa among warfarin users. A similar risk of PCa was found among warfarin users and the general population, and no difference in risk was found between warfarin and other anticoagulants.
Disclosure statement
We declare the following conflicts of interest: P. T. T. Kinnunen: none; T. J. Murtola: paid consultant for Astellas and Janssen-Cilag, lecture fees from Janssen-Cilag, Abbvie and MSD; K. Talala: none; K. Taari: consulting fee from Abbvie, lecture fee from GlaxoSmithKline, research funding from Medivation, travel support from Astellas and Orion; T. L. J. Tammela: paid consultant for Astellas, GlaxoSmithKline, Pfizer, Orion Pharma and Amgen; A. Auvinen: lecture fee from MSD, paid consultant for Epid Research Inc.