Likely causes: Leg or arm injury, such as a sprained ankle…recent hospitalization or surgery…long period of inactivity, such as a plane ride.
But it could be a sign of: Breast, pancreatic, ovarian and many other cancers. A blood clot (a symptom of deep vein thrombosis, or DVT) is a common problem affecting 900,000 Americans yearly. But D VT is not commonly understood as a potential early warning sign of cancer and so is often overlooked as a cancer symptom, even though as many as one in 10 patients with an unexplained blood clot may have some kind of cancer.
What to do: If you have a blood clot (typically signaled by a sudden, painful swelling of an arm or a leg) without any of the common triggers, talk to your doctor about a workup for cancer. This is an early warning sign that often is missed.
Source: Bottom Line Personal June 2015