A blood clot (also called a thromboembolism) is a serious side effect of cancer and cancer treatment. A blood clot that develops in a vein (a blood vessel that carries blood to the heart) is called a venous thromboembolism (VTE). It may develop in any vein but happens most often in the legs, thighs, or pelvis (lower abdomen). This is called deep vein thrombosis (DVT). A pulmonary embolism (PE) is a blood clot that has traveled to the lung from another place in the body. A PE can be life-threatening.

Blood clots are common in patients with cancer. Many patients are not aware of the risks, symptoms, and signs of a blood clot. The risks for a blood clot are listed below, followed by the signs and symptoms. If you have questions and concerns about the risks and symptoms listed below, it’s important to talk with your doctor.

Risk factors for blood clots

• Cancer, especially cancers of the lung, kidney, brain, digestive system, female reproductive system (such as uterine cancer), and blood (such as leukemia and lymphoma)
• Metastatic cancer (cancer that has spread to other parts of the body from where it started)
• Cancer treatment, including surgery lasting longer than one hour, chemotherapy, radiation therapy, and hormone therapy. Antiangiogenic drugs (drugs that block the formation of new blood vessels), such as thalidomide (Synovir, Thalomid) and lenalidomide (Revlimid), may increase the risk of blood clots.
• Treatment with erythropoiesis stimulating agents (drugs that help the body make more red blood cells), such as epoetin (Epogen, Eprex, Procrit) and darbepoetin (Aranesp)
• Being in the hospital, because most patients in the hospital can't be physically active and need to stay in bed or are unable to get out of bed  
• A history of blood clots
• Having other diseases or conditions in addition to cancer, such as obesity, infection, kidney disease, lung disease, or a blood clot in an artery (a blood vessel that carries blood away from the heart)
• Older age
• Race/ethnicity (the risk is higher for black people and lower for people of Asian-Pacific Islander descent)
• A condition that is inherited (comes from a relative, such as your mother or father), such as sickle cell disease, or a blood clotting disorder such as factor V Leiden mutation (a condition that causes too much blood clotting)

Symptoms and treatment

The symptoms of DVT include pain, swelling, and redness of the calf, leg, or thigh. The symptoms of PE include shortness of breath, chest pain, breathing fast, rapid heartbeat, coughing up blood, and fainting.

Blood clots can be prevented and treated with drugs. Anticoagulants are drugs that help break up blood clots or stops clots from happening. Coagulation is the term used to describe the clotting of the blood. Anticoagulants may increase a person's risk of bleeding, but they are safe for most people. Typical anticoagulants include heparin, dalteparin (Fragmin), enoxaparin (Lovenox), fondaparinux (Arixtra), tinzaparin (Innohep), and warfarin (multiple brand names). Some of these drugs are taken orally (by mouth) in a pill form and others are given subcutaneously (an injection given under the skin). A doctor may add a non-drug method, called a mechanical method, to the drug treatment to prevent blood clots. Mechanical methods include graduated compression stockings (a type of support hose); intermittent pneumatic compression (squeezing the legs through a sleeve connected to a machine), and mechanical foot pumps.