Tagalakis V et al. (2007) Use of warfarin and risk of urogenital cancer: a population-based, nested case-control study. Lancet Oncol 8: 395–402

Secondary analyses in studies of warfarin treatment for venous thromboembolism suggest that warfarin use is associated with a reduced risk of cancers, particularly urogenital cancers; however, some reports have failed to find such an association. Tagalakis et al., therefore, carried out a population-based, nested case–control study in Saskatchewan, Canada, to assess whether warfarin use is associated with a decreased risk of urogenital cancer.

The source population (aged ≥50 years with no history of cancer since 1967) was derived from beneficiaries of Saskatchewan Health who were eligible for prescription drug benefits between 1 January 1981 and 31 December 2002. During this period 19,412 cases of urogenital cancer (11,502 prostate, 3,424 bladder, 1,601 kidney, 1,800 uterine and 1,085 ovarian) were diagnosed in the source population. A total of 116,470 controls matched for age and sex and free from cancer (six for each case) were randomly selected from the source population. After adjustment for potentially confounding effects of prescription drugs, no significant association was found between warfarin use and the risk of any of these urogenital cancers apart from prostate cancer. Compared with men who never used warfarin, long-term cumulative warfarin use (≥1 prescription per year in the 4 years immediately before cancer diagnosis) significantly decreased the adjusted incidence rate ratio of prostate cancer (0.80, 95% CI 0.65–0.99).

The authors conclude that the anticancer effect of long-term warfarin use for prostate cancer should be investigated further to comprehensively assess the effects of confounders on this association.