Preventing and Treating Blood Clots

To help doctors give their patients the best possible care, the American Society of Clinical Oncology (ASCO) asks its medical experts to develop recommendations for specific areas of cancer care. In 2007, ASCO developed a clinical practice guideline about preventing and treating blood clots for people with cancer. These recommendations were updated in 2013 to reflect new research. This guide for patients is based on ASCO's recommendations.

Key Messages:

  • Blood clots often occur for many reasons in people with cancer, especially in those with certain types of cancer or cancer that has spread.
  • Blood clots can be prevented and treated with medication.

Talk with your doctor about your risk of developing a blood clot and the steps you can take to prevent one.


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.


ASCO recommends that doctors determine the risk of a blood clot for all patients, especially before starting or changing chemotherapy. ASCO also recommends the following for preventing and treating blood clots for patients with cancer:

  • Most patients with cancer who are in the hospital should receive treatment with an anticoagulant to prevent blood clots during their hospital stay.
  • Many patients who have to stay in the hospital for just a few days, such as for a minor procedure, do not need blood clot prevention, except for those patients who have a high risk of blood clots.
  • To prevent blood clots, heparin or low doses of aspirin are recommended for patients with multiple myeloma who are receiving both antiangiogenic drugs and chemotherapy and/or the drug dexamethasone (multiple brand names).
  • Patients who will have major surgery for cancer should receive treatment to prevent blood clots before surgery, continuing for at least seven to ten days after surgery. Treatment may continue for up to four weeks for patients who have a higher risk of blood clots.

Heparin is recommended to treat DVT and PE for the first five to ten days, as well as long-term (longer than six months) prevention of blood clots.

What This Means for Patients

For people with cancer, especially those who are in the hospital, developing a blood clot is a serious risk. However, blood clots can often be prevented with anticoagulant medication. These medications are generally safe, although there is a small risk of bleeding. For patients who develop a blood clot (either a deep vein thrombosis, pulmonary embolism, or both), the same drugs that are used to prevent clots are given as a treatment. Talk with your doctor to learn more about your individual risk of developing a blood clot, how blood clot prevention will be included in your overall treatment plan, and what treatments are available if you do develop a blood clot.

Questions to Ask the Doctor

To learn more about your risk of blood clots, consider asking your doctor the following questions:

  • Do I have a higher risk of a blood clot? How is my risk of developing blood clots determined?
  • What can be done to prevent a blood clot before it starts?
  • What are the signs and symptoms of a blood clot?
  • If I have a blood clot or have had them before, what treatment do you recommend?
  • How long will I need this treatment?
  • What is my risk of bleeding with such treatment? Are there other side effects?
  • What health conditions or medications may interfere with the treatment for blood clots?
  • Who should I call if I have concerns about a symptom?
Helpful Links

Read the entire clinical practice guideline at

Cancer.Net Guides to Cancer

Side Effects of Cancer Surgery

Bleeding Problems

About ASCO's Guidelines

To help doctors give their patients the best possible care, ASCO asks its medical experts to develop evidence-based recommendations for specific areas of cancer care, called clinical practice guidelines. Due to the rapid flow of scientific information in oncology, new evidence may have emerged since the time a guideline or assessment was submitted for publication. As a result, guidelines and guideline summaries, like this one, may not reflect the most recent evidence. Because the treatment options for every patient are different, guidelines are voluntary and are not meant to replace your physician’s independent judgment. The decisions you and your doctor make will be based on your individual circumstances. These recommendations may not apply in the context of clinical trials.

The information in this patient guide is not intended as medical or legal advice, or as a substitute for consultation with a physician or other licensed health care provider. Patients with health-related questions should call or see their physician or other health care provider promptly and should not disregard professional medical advice, or delay seeking it, because of information encountered in this guide. The mention of any product, service, or treatment in this guide should not be construed as an ASCO endorsement. ASCO is not responsible for any injury or damage to persons or property arising out of or related to any use of this patient guide, or to any errors or omissions.

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