Cancer raises blood clot risk by sevenfold

Cancer greatly increases the risk that the patients will develop a blood clot in a vein (venous thrombosis), especially in recently diagnosed patients, patients with cancer that has spread to distant sites (metastases), and those with certain genetic mutations, according to Dutch researchers. While anticoagulant therapy might be beneficial, they say, the associated increased risk of bleeding has to be considered.

The findings, reported in the Journal of the American Medical Association, are based on a survey of 3220 consecutive patients who were diagnosed with a blood clot in the leg or lung between 1999 and 2002 at six clinics in the Netherlands.

The group of 2131 partners of the patients was used as a comparison.

Cancer increased the risk of venous thrombosis 6.7-fold, Dr. Frits R. Rosendaal and colleagues, from Leiden University Medical Center, note. Patients with cancers of the blood system had the highest increased risk - 28.0-fold - followed by patients with lung cancer and GI cancer.

The highest risk of clots occurred within 3 months of the cancer diagnosis. At this point, cancer patients were 58.2-times more likely to develop venous thrombosis than were controls.

The presence of distant metastases raised the risk of thrombosis, over and above that seen with cancer alone, by 19.8-fold.

Furthermore, cancer patients who were also carriers of the factor V Leiden mutation or the prothrombin 20210A mutation were 12-times more likely to develop a clot than healthy non-carrier patients.

The author suggest that future studies address the issue of giving preventive anticoagulant therapy to patients with cancer in the first months after the diagnosis and to patients with distant metastases. "However, since these patients also have an increased risk of hemorrhage, this needs to be cautiously evaluated."

SOURCE: Journal of the American Medical Association, February 9, 2005.