A large observational study from Norway has found a big reduction in cancer rates for those on warfarin:
medscape.com/viewarticle/88...
For those with AF or Flutter there is a reduction of 40% in cancer risk.
The authors note that the "well-known challenges of warfarin dosing that necessitate regular monitoring have fuelled a transition to new oral anticoagulants. An unintended consequence of this switch to new oral anticoagulants may be an increased incidence of cancer, which is an important consideration for public health"