McMaster University

McMaster University

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Health Sciences

New England Journal of Medicine publishes Canadian-led study showing significant reduction in blood clots in cancer patients

Anticoagulant injections significantly reduced incidence of recurrent blood clots, which are common and serious complications of cancer

Published: July 10, 2003

McMaster University researchers announced today that cancer patients with newly diagnosed blood clots who took an anticoagulant (blood thinner) injection developed half as many recurrent blood clots compared to patients taking standard oral anticoagulant therapy. These findings are published in today's issue of the New England Journal of Medicine.

Health Canada estimates that 140,000 patients will develop cancer in Canada in 2003. Thrombosis (or blood clots) is a common complication in patients with malignant disease, with up to 15 percent of patients developing a clot with major symptoms. The occurrence of a blood clot can have a significant impact on a cancer patient's quality of life and in some instances can be life-threatening.

The landmark CLOT study (Randomized Comparison of Low-Molecular-Weight Heparin versus Oral Anticoagulant Therapy for the Prevention of Recurrent Venous Thromboembolism in Patients with Cancer), which was developed and led by a team of Canadian investigators at McMaster University in Hamilton, looked at the use of dalteparin, an anticoagulant injection, compared to standard oral anticoagulant therapy for treating cancer patients with symptomatic, newly diagnosed deep vein thrombosis (blood clots in large veins, usually in the legs) and/or pulmonary embolism (blood clots that have travelled to the arteries of the lungs). Dalteparin-treated patients experienced 52 percent fewer recurrent clots over the six-month study period. Additionally, they showed no significant increase in the incidence of bleeding.

Patients who take traditional oral anticoagulants like warfarin must undergo frequent blood tests and dose adjustments to maintain appropriate therapeutic levels of the anticoagulant in the blood. This is because these agents interact with food and other medications. Too little of the blood thinner may not prevent clotting; too much could cause excessive bleeding. The safe and effective range is very narrow.

Dalteparin is a low-molecular-weight heparin that is injected under the skin. Unlike oral anticoagulants, it has a predictable blood-thinning effect even if a patient cannot hold down food or is taking several other medications, as is often the case for cancer patients. Thus, blood tests to monitor anticoagulant activity are unnecessary.

Due to their disease and the effects of cancer treatment, cancer patients are more than three times more likely than non-cancer patients to develop recurrent blood clots, and twice as likely to experience major bleeding while on traditional oral anticoagulant therapy. Safe long-term anticoagulant treatment is critical, but complicated, in cancer patients.

"Preventing clots with oral anticoagulants can be challenging in cancer patients because one in six cancer patients will develop recurrent blood clots despite this standard treatment," said lead author Agnes Lee, M.D., McMaster University, Ontario. "The CLOT study showed that long-term treatment with dalteparin is feasible, safe and more effective in this high-risk patient group. The results represent a major medical advance in the supportive care of cancer patients."

"There is a great need for an anticoagulant that provides long-term protection against clots but doesn't further burden the cancer patient," said co-author Mark Levine, M.D., McMaster University, Ontario. "The occurrence of thrombosis in a patient with cancer complicates the clinical management of a patient who may already have a poor quality of life. The prevention of recurrent thrombosis is key. Long-term dalteparin substantially reduced the risk of recurrent thrombosis and was safe."

In Canada, dalteparin is indicated for the treatment of deep vein thrombosis and prophylaxis of thrombosis in conjunction with surgery. Dalteparin, like other anticoagulants, should be used with caution in patients who have an increased risk of bleeding and those with hepatic insufficiency, renal insufficiency or a history of gastrointestinal ulceration.

The study was funded by a grant from Pharmacia Corporation, a wholly owned subsidiary of Pfizer Inc.

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