A population based study by Dr. Tagalakis and colleagues suggest that a marginally lower risk of prostate cancer (CaP) in men on 4 years of warfarin therapy. This report appears in the May 2007 issue of the Lancet Oncology.
The population source was the Saskatchewan, Canada Cancer Registry and Saskatchewan Health, which comprise 99% of the one million Saskatchewan residents. ICD codes identified patients between 1981 and 2002 with any urogenital cancer to include prostate (11,502), bladder (3,424), kidney (1,601), uterine (1,800), and ovarian (1,085). For each case, six randomly selected controls without cancer were matched. Data on warfarin use was obtained from an outpatient prescription drug database. Warfarin ever-use and cumulative use were correlated with cancer risk. Conditional logistic regression was used to calculate matched odds ratios (OR).Men with CaP and their matched controls had the highest prevalence of ever use of warfarin before the index date. This is consistent with the higher use of warfarin in men and increased use with increasing age. A marginally lower risk of CaP was found for men with 4 years of warfarin use compared with those who did not receive warfarin. Four years of warfarin usage in the 5-year period immediately preceding the index date was associated with a rate ratio of 0.80. A trend towards a decreasing rate ratio of CaP was found with increasing duration of warfarin use during years 2 through 5. For warfarin use, 76-100% of the time the rate ratio was 0.80 during year 2, 0.76 during year 3, 0.67 during year 4, and 0.81 during year 5. No other urogenital cancer was found to have an association with warfarin use. What is not assessed in this database is whether a selection bias against doing a prostate biopsy existed for men with an increased PSA who would require a change in anticoagulation regimen or temporary cessation of warfarin, while some of the other urogenital tumor can be diagnosed radiographically or without stopping anticoagulation. This would be potentially biased by the more indolent natural history of CaP.(Source: Lancet Oncology : Canada Cancer Registry : May 2007.)