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Background:

Several studies have analyzed the effect of anticoagulants on cancer survival, with varying results. This study aimed to assess the effect of warfarin on survival in patients with colorectal cancer (CRC) in relation to timing of warfarin initiation.

Methods:

Data on 10,051 individuals aged >45 years in the Vastra Gotaland Region of Sweden, and diagnosed with CRC between 2000 and 2009, were obtained from the Swedish National Cancer Register. Those who received warfarin treatment (n= 1,216) during the study period were labeled cases and those who did not (n= 8,873) were labeled controls. For statistical analysis, National Cancer Register data were merged with mortality data from the Swedish National Cause of Death register and data from the regional warfarin treatment register.

Results:

Hazard rates for CRC-specific mortality were lower in cases than in controls. When warfarin was used for any reason at any time, cases had a significantly lower CRC-specific mortality than controls among both women (hazard ratio [HR] 0.71; 95 % confidence interval [CI] 0.59-0.85; p = 0.0002) and men (HR 0.61; 95 % CI 0.52-0.72; p < 0001). Warfarin treatment after CRC diagnosis reduced CRC-specific mortality by 80 %; however, when warfarin was given before or >5 years after diagnosis, CRC-specific mortality did not significantly decrease. The number needed to treat to avoid one death was four.

Conclusion:

Use of warfarin early after diagnosis in patients with CRC was associated with improved survival.