Bad Block

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CURE, Summer 2010, Volume 9, Issue 2

Being aware of the dangers of deep vein thrombosis

After an injury, the body stops bleeding by clotting the blood. When a blood clot develops in a vein in the leg or pelvic region, it’s called deep vein thrombosis (DVT). The clot can then dislodge, travel through the bloodstream, and get stuck in blood vessels of the lung—known as a pulmonary embolism—which can be life-threatening.

In cancer patients, research has shown around 50 percent have DVT at some point. Unfortunately, DVT is underdiagnosed and undertreated. Agnes Lee, MD, director of the thrombosis program at the University of British Columbia and Vancouver Coastal Health, says most cases of DVT are missed because the symptoms are nonspecific and often attributed to other conditions.

Symptoms of DVT include pain, swelling, tenderness, and discoloration and/or prominent veins in the calf or leg. Sometimes there are no symptoms.

Traditionally, patients with blood clots are treated with anticoagulants, or “blood thinners.” Heparin followed by warfarin (brand names include Coumadin and Jantoven) was previously the standard treatment, but these drugs, given as pills, require constant patient monitoring, and the dosage has to be continuously reevaluated, especially when other medications are being used since drug interactions can occur.

“If you underdose patients, they’ll have more clots. If you overdose them, they’ll end up with more bleeding,” says Lee. “It’s a difficult tightrope for patients and physicians to walk on.”

Now, Lee says, the preferred treatment is low molecular weight heparin, which is a class of drugs given by injection. LMWHs include Lovenox (enoxaparin), Fragmin (dalteparin), and Innohep (tinzaparin). Similar to insulin for diabetes patients, patients self-inject once a day. Unlike the heparin-warfarin combo, patients on LMWHs don’t need to be monitored. However, for some patients, warfarin may still be a relatively safe and less costly option.

Patients are treated with blood thinners for a minimum of three months. High-risk patients may be on treatment for much longer or permanently. Patients on blood thinners should avoid situations that can lead to serious injury or bleeding.

Some cancer patients tout aspirin as a way to manage DVT, but Lee says there is no evidence it works, and feels it could even cause more bleeding. While aspirin in low doses is used to prevent arterial blood clots, heart attacks, and strokes for high-risk individuals, it has little effect on treating DVT, which is a clot in the veins as opposed to the arteries.

“Most people don’t distinguish blood clots in their legs from heart attacks or strokes,” Lee says. “It is important for patients to know the difference, since the treatment and outcomes are not the same.”

Hospitalized patients are sometimes temporarily treated with a preventive blood thinner. But since most of the risk factors for DVT are associated with cancer, the best thing a patient can do, Lee says, is be aware of the signs and symptoms of DVT and tell a doctor if those symptoms arise.

General tips to reduce the risk of DVT include moving around during inactive periods, losing weight, and quitting smoking.

The reasons for developing DVT range from the effects of treatment to the nature of the cancer itself. Lee says most chemotherapy drugs can be associated with a risk of DVT because they can damage blood vessel linings or activate clotting elements in the blood and platelets. Hormonal therapies and antiangiogenesis drugs are common culprits, as are 5-fluorouracil, platinum-based agents, and L-asparaginase, which is used to treat acute lymphoblastic leukemia.

Certain types of cancers, including pancreatic, ovarian, stomach, and lymphoma, have also been associated with a higher risk. These tumors produce substances that promote clotting, Lee says.

Other risk factors include having a port-a-cath, blood transfusions, recent surgery, serious infections, injury or surgery to the legs, spine, or hips, and/or being subjected to bed rest.