I have had two arm dvt's. one from birth control and one unexplained. i've heard these unexplained ones can be from occult cancer? how likely is this?

Low risk: Much more likely that you have a clotting abnormality where your blood clots too easily.There are a number of these conditions, and more common amongst women who have a clot on birth control. I urge you to set up an appointment with a hematologist (doctor who specializes in blood problems) and have a full evaluation done. Blood clots can be serious and even life-threatening. And if you smoke-stop!

Unlikely in you.: Dvt is usually the result of 3 possibilities-venous stasis such as occurs with immobility(casts, post surgery, bed ridden), venous trauma with injury to a vein wall such as what occurs from iv's or catheter insertions, and those patients that are hyper coagulable(have increase risk of clotting) such as those on bcp, those with cancer or those with clotting disorders. You should have a clotting w/u.