There's a paper just out on GI bleeding on anti-coagulants:
medscape.com/viewarticle/92...
Apparently there is a 10-24 times risk of colorectal cancer if you bleed from the lower GI tract whist on anticoagulants.
It is actually a good news story as it's not the anticoagulant causing the cancer. The anticoagulant causes notable bleeding earlier than would otherwise be the case. Consequently the cancer can be treated earlier.
The key message is that if you have GI bleeding, don't just pass it off as the anticogulant, you must have an endoscopy to see if there's something there.