Preventing and Treating Blood Clots

January 20, 2015

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 2013, ASCO updated the clinical practice guideline about preventing and treating blood clots for people with cancer to reflect new research. These recommendations were reviewed again in 2015, and the latest research continues to support the previous recommendations. 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 venous thromboembolism (VTE) is a blood clot that develops in a blood vessel called a vein that carries blood to the heart. It may develop in any vein but happens most often in the legs, thighs, or pelvis. 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, which is 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. Drugs called antiangiogenic 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 drugs called erythropoiesis stimulating agents 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 a blood vessel called an artery 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, meaning it is passed down from parent to child in a family, such as sickle cell disease, or a blood clotting disorder such as factor V Leiden mutation, which is 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 stop 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 the following:

  • Heparin
  • Dalteparin (Fragmin)
  • Enoxaparin (Lovenox)
  • Fondaparinux (Arixtra)
  • Tinzaparin (Innohep)
  • Warfarin (multiple brand names).

Some of these drugs are taken orally as a pill that is swallowed, and others are given as an injection given under the skin, called a subcutaneous injection.

A doctor may add a non-drug method, called a mechanical method, to the drug treatment to prevent blood clots. Mechanical methods include the following:

  • Graduated compression stockings, which are a type of support hose
  • Intermittent pneumatic compression, which is squeezing the legs through a sleeve connected to a machine
  • 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 for preventing blood clots for longer than six months.

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 deep vein thrombosis, and/or a pulmonary embolism, 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

Guides to Cancer

Side Effects of Cancer Surgery

Clotting Problems

When to Call the Doctor During Cancer Treatment