Blom JW et al. (2005) Malignancies, prothrombotic mutations, and the risk of venous thrombosis. JAMA 293: 715–722

The Multiple Environmental and Genetic Assessment (MEGA) study of risk factors for venous thrombosis has confirmed the link between cancer and venous thrombosis, and has begun to decipher which patients are at risk.

This population-based study in the Netherlands included 3,220 consecutive patients who experienced a first pulmonary embolism or deep venous thrombosis of the leg. A further 2,131 participants, all of whom were partners of the patients, were included as controls. All participants completed a questionnaire about acquired risk factors for venous thrombosis in the period before the index date. This was then followed up by interview three months after each patient discontinued anticoagulation therapy. At this time, a blood sample was taken to allow testing for factor V Leiden and prothrombin 20210A mutations.

Comparison of the data from patients and control participants revealed a sevenfold higher risk of venous thrombosis in those with a malignancy than in those without. Analysis by tumor type showed that hematological malignancies carried the highest risk, followed by lung and gastrointestinal tumors. It was not possible, however, to measure the risk associated with some rare tumors. The risk of venous thrombosis was increased by a factor of more than 50 in the first few months after diagnosis of cancer, and patients with distant metastases were at higher risk than those without. Finally, the risk of venous thrombosis was higher still among carriers of the factor V Leiden or prothrombin 20210A mutations.

Concluding that cancer patients were at a significantly increased risk of venous thrombosis, the authors propose that certain patients might benefit from prophylactic anticoagulation treatment. The benefits of such treatment, however, would need to be balanced carefully against the increased risk of hemorrhage.