Blood Clotting (Thrombosis)

Blood clotting, or coagulation, is a normal process that prevents excessive blood loss when you have a cut or an injury. Platelets combine with specialized proteins in the blood called clotting factors, forming clots that can stop bleeding at the injured site. These small clots eventually dissolve after your injury heals.

Abnormal clotting can sometimes lead to the formation of a deep vein thrombosis (DVT) — a blood clot that forms in a deep vein, usually in the leg. A DVT that detaches from a vein in another part of the body and travels to the lungs is called a pulmonary embolism.

People with cancer are at increased risk of developing these dangerous blood clots. Research has shown that there is a clear connection between cancer and thrombosis, because some of the genetic changes that cause cancer also increase the activation of clotting factors. In addition, many of the chemotherapy drugs used to combat cancer can increase the activation of clotting factors.

Having a preexisting condition that increases the activation of clotting factors could further increase your risk of developing a blood clot during cancer treatment. Conditions that may increase your risk of blood clots include inherited disorders such as the Factor V Leiden mutation, prothrombin gene mutation, protein C deficiency, protein S deficiency, and antithrombin III deficiency.


DVT and pulmonary embolisms reduce the flow of oxygenated blood throughout the body. However, many people with a blood clot in the legs or lungs do not feel any symptoms until the problem becomes life threatening. When symptoms occur, they may include:

  • sudden pain and swelling in the legs
  • sharp chest pain, fast pulse, bloody cough, shortness of breath, sweating, fever
  • severe abdominal pain, vomiting, diarrhea

Tell your doctor immediately if you notice any of these symptoms.

Diagnosing Blood Clots

Many blood clots are found incidentally, following a medical scan during cancer diagnosis or treatment. At other times, a patient may report symptoms that could indicate a blood clot during a routine follow-up exam. If a blood clot is suspected, our team may perform one or more of the following tests:

  • Additional blood tests to measure the rate at which your blood clots and to identify protein deficiencies that prevent clotting
  • A CT scan of the lungs to look for a pulmonary embolism
  • Venous Doppler ultrasound to look for blood clots in your lower extremities

Our team can most effectively manage these problems without interrupting your cancer therapy by diagnosing and treating a blood clot as early as possible.

Treating Blood Clots

Memorial Sloan Kettering provides a variety of treatments for patients who develop blood clots during cancer therapy. Our hematologists are experts in determining the best approach, and will work with your primary cancer care team to develop a plan that is coordinated with other treatments you may be receiving. Our state-of-the-art Anticoagulation Clinic is also staffed with nurse practitioners who are experienced in taking care of patients receiving blood thinner treatments, including both oral and injectable anticoagulant medications.

Treatment for a blood clot may include one or a combination of the following:

  • Anticoagulants (Blood Thinners) — Heparin or other medications that block the activation of clotting factors are given intravenously or by injections under the skin.
  • Inferior Vena Cava Filter — The inferior vena cava (IVC) is the large vein that delivers blood from the legs to the heart. Our experienced interventional radiologists insert a special filter into the IVC, capturing clot fragments before they travel to the heart and lung. The filter is removed when it is no longer needed.
  • Thrombolytics (Clot Busters) — Medications such as tissue plasminogen activator (tPA) can rapidly dissolve clots. These drugs are given through a catheter.
  • Thrombectomy — Surgery is sometimes necessary to remove a blood clot that becomes life threatening and does not respond to other treatments.

Doses of anticoagulant and thrombolytic medications need to be handled carefully so that they do not increase your risk of bleeding. Hematologists and nurse practitioners in our Anticoagulation Clinic frequently monitor and adjust blood levels of these medications to reduce the risk of bleeding, especially before surgical procedures.

Our hematologists are helping to develop a new class of oral anticoagulant medications that may cause fewer bleeding problems than currently available medications. Researchers at Memorial Sloan Kettering are also evaluating a variety of chemotherapy drugs to determine which ones are more likely to cause blood clots.

Your doctor may recommend additional strategies to prevent blood clots during and after treatment, such as wearing compression stockings and avoiding long airplane trips. In addition, our team offers education and information about the many prevention, screening, and wellness services available at Memorial Sloan Kettering.