Cancer risk in long-term users of vitamin K antagonists: A population-based case-control study

Some evidence suggests that long-term use of vitamin K antagonists (VKAs) has a cancer chemopreventive effect. Such an
effect would have considerable implications in terms of understanding tumor biology. To evaluate if long-term VKA treatment
influences the risk of developing cancer, we performed a matched case–control analysis. We used data from four Danish
nationwide registers. Cases were all Danish individuals with a first-time cancer diagnosis (except nonmelanoma skin cancer)
between 2000 and 2009. For each case, eight controls, matched by birth year and gender, were selected from the source
population by risk-set sampling. Long-term VKA use was defined as exposure to VKA for a period of 3 or more years.
Conditional logistic regression was used to compute odds ratios (ORs) for cancer associated with long-term VKA exposure,
adjusting for potential confounders. Prespecified subanalyses were performed for selected cancer sites, subgroups and
measures of exposure. A total of 238,196 cases and 1,713,176 controls were included. The adjusted OR for cancer associated
with long-term VKA exposure was 0.99 (95% CI: 0.95–1.02). Long-term VKA use was associated with increased ORs for
alcohol- or obesity-related cancer sites, whereas we observed a decreased risk of prostate cancer (OR: 0.86; 95% CI:
0.78–0.95). Our study does not support a general chemopreventive effect of VKA drugs. However, in accordance with findings
from previous studies, we found an inverse association between use of VKA and prostate cancer.