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Unexplained clot in vein may be cancer harbinger

A patient who develops a blood clot in a leg vein for no apparent reason may be destined to develop cancer, researchers from Italy and the Netherlands have concluded.

The clotting is known as deep-vein thrombosis. In tests of 145 patients who developed the clot for no obvious reason, Dr. Paolo Prandoni of the University Hospital of Padua and his colleagues found that more than 7 percent developed a tumor within two years.

Among 105 patients whose clot was probably caused by problems such as leg injury or a protein deficiency, only 2 percent subsequently had cancer.

If a second unexplained clot developed, the risk of cancer was even higher, the team found.

The findings do not explain the link between the clots and cancer, a connection first suggested in 1868.

In an editorial in today's New England Journal of Medicine, where the study appears, Drs. Roy L. Silverstein and Ralph L. Nachman of the Cornell University Medical College in New York said doctors should suspect cancer in patients "with deep-vein thrombosis and no identifiable risk factor."

Generally, if a tumor is found early, the likelihood of a cure is highest.