The risk of developing cancer is more than three times higher in the first six months following the diagnosis of acute arterial thrombosis, or a blood clot in the leg, say researchers at Denmark's Aarhus University.

Patients with the most acute type of thrombosis in the leg, known as an arterial thrombosis, risk developing diseases that are far worse than the blood clot itself.

"It is especially, but not only, the smoking-related forms of cancer that show up after the arterial thrombosis, said researcher Jens Sundbøll. "The risk is highest for lung and pancreatic cancer, both of which are related to smoking. However, other forms of cancer such as colon cancer and leukemia are also overrepresented."

The risk falls steadily following the first six months to a 40 percent increased risk. After a year, the increased risk of cancer remains steady at 15 percent.

An ordinary venous blood clot causes the leg to swell, contract and become warm and red, but symptoms of an arterial blood clot are almost the opposite. The leg becomes pale and cold, and Sundbøll says doctors should remember the five p's: pallor, pulselessness, pain, paresis/paralysis as well as paraesthesia ("pins and needles sensation").

"If the arterial thrombosis is not correctly treated within a short period of time, the patient typically loses a leg," Sundbøll said.

Sundbøll notes that hospitalizations in connection with arterial blood clots are an obvious opportunity to question patients about early signs of the various cancers that the arterial blood clots are now shown to be markers for:

"It is well known that early treatment is crucial for the prognosis of many types of cancer, and our findings show that an arterial thrombosis in the leg is associated with an increased risk of cancer to the same degree as a deep venous thrombosis," Sundbøll said. "This is an important finding, which clinicians should integrate into their deliberations.

"Hospitalization for an arterial thrombosis in the leg is an obvious opportunity to carry out an opportunistic screening for cancer, which I believe should be considered, just as for patients presenting with a deep venous thrombosis."

The study was published in the journal Circulation.