Cancer and the risk of blood clots

Cancer can increase the risk of developing blood clots. Doctors often give blood clots different names depending on where they start. You may hear them say:

  • deep vein thrombosis (DVT)
  • pulmonary embolism (PE)
  • venous thromboembolism (VTE)

Blood clots can be very serious. Contact your doctor or get advice from 111 if you think you have a blood clot.

What is a blood clot?

A blood clot is a collection of blood that can form inside a blood vessel (a vein or an artery). It can block the normal flow of blood. The medical name for a blood clot is thrombus.

Blood clots can develop in different parts of the body. When a blood clot forms in the deep veins of the leg it is called a deep vein thrombosis (DVT).

Part or all of a DVT can break off and travel around the body. It may travel through your heart to block part or all of the blood supply to the lungs. If this happens, it’s called a pulmonary embolism (PE). DVTs and PEs together are sometimes called venous thromboembolism (VTE).

Doctors can successfully treat most blood clots when diagnosed. So it's important to know about the symptoms of blood clots and report them to your doctor or nurse immediately.


Common symptoms of blood clots include:

  • unexplained pain in your leg or arm

  • redness and swelling in your leg - this may be just in the calf or include the whole of your leg

If a blood clot has moved to your lungs (a pulmonary embolism), the symptoms include: 

  • feeling breathless - this might start suddenly or increase over time

  • pain in your chest or upper back which gets worse when you breathe in

  • coughing up blood

  • feeling lightheaded

Call 999 or go to A&E if you have symptoms of a blood clot in your lungs.

Who is at risk of blood clots?

People with cancer have a higher risk of developing blood clots. Researchers think that up to 20 out of every 100 people with cancer (up to 20%) develop a blood clot at some point.

There are a number of reasons for this: 

The cancer itself

People with cancer often have sticky blood. This may be because cancer cells make chemicals that stimulate the body to produce clotting factors.

Clotting factors are proteins made naturally by the liver. They combine with platelets to form blood clots and help us stop bleeding.

The type of cancer you have

You are at a higher risk of developing blood clots if you have one of the following types of cancer:

  • pancreas
  • womb
  • lung
  • stomach
  • kidney
  • brain
  • bladder

Also, the risk is higher in cancers that have spread to nearby lymph nodes or other parts of the body.

Cancer treatments

Certain cancer treatments can increase the risk of developing blood clots. These include:

  • the chemotherapy drug cisplatin
  • tamoxifen which is a type of hormone treatment for breast cancer
  • L-asparaginase
  • thalidomide
  • lenalidomide

Your doctor will explain if the treatments you are having increase the risk of blood clots. They make sure the benefits of these treatments outweigh the risks.  

Blood clots can also form in long lines such as central lines and PICC lines. These lines usually stay in your veins for many months. So you don’t need to have needles into your hand or arm each time you have cancer drug treatment. 

Being less active

Cancer and its treatment can make you feel very ill. You can feel too tired and weak to move around as much. The blood flow in your leg veins depends on the squeezing of the veins by leg muscles when you walk. Immobility reduces the blood flow in the legs and blood can stagnate in the legs and become sticky.

So moving around helps reduce the risk of clots. As does doing exercises with the calf muscles such as moving your foot up and down.

After cancer surgery, you may not be able to move around much. Your nurses will give you a pair of elastic stockings to wear. These help to prevent blood clots. You need to wear these until you are moving around fully. This may be for a few weeks after your operation.

Long journeys, such as long haul flights, or long bus or car journeys can also increase the risk of clots.

Other factors

Other factors that increase the risk of developing a blood clot include:

  • taking the oral contraceptive pill or hormone replacement therapy (HRT)
  • certain medical conditions such as diabetes or heart disease
  • smoking
  • being overweight
  • having an inflammatory condition such as Crohn's disease or rheumatoid arthritis

Treating blood clots

Treatment for blood clots is usually drugs that thin your blood (anticoagulants). They don't break up an existing clot but prevent it from growing bigger and others forming. This allows the body to gradually break the clot down and reabsorb it.

You usually take anticoagulants for 3 to 6 months.

The most common types of anticoagulants are:

Direct oral anticoagulants (DOACs)

These include:

  • apixban
  • dabigatran
  • edoxaban
  • rivaroxaban

These are new types of blood thinners that mean you don't need to have regular blood tests. They are also used to prevent stroke and to treat blood clots in people who don't have cancer.

Low molecular weight heparins

These include:

  • dalteparin
  • enoxaparin
  • tinzaparin

You have low molecular weight heparins as an injection under the skin (subcutaneously). You may need regular blood tests.


Warfarin comes as a tablet. They are a type of anticoagulant called vitamin K antagonist (VKA). Doctors most often prescribe warfarin to people who have a heart condition called atrial fibrillation. This causes an irregular and fast heart rate.

It takes several days for warfarin to work so you may also have heparin first. You may take warfarin for a few weeks or months. You have regular blood tests to check that your blood is not getting too thin or too thick. 

Unfractionated heparin

This is a fast acting heparin. You usually have it directly into your bloodstream (intravenously). You might have it when you're first diagnosed with a blood clot, especially if your kidneys are not working very well.

Reducing the risk of a blood clot while in hospital

The National Institute of Health and Care Excellence (NICE) has guidance about reducing the risk of blood clots for people in hospital.

When you are in hospital, your doctor or nurse will assess your risk of developing blood clots. They will suggest you have preventative treatment if you are at higher risk of developing blood clots. This might include:

  • taking drugs that thin your blood (anticoagulants)
  • wearing elastic stockings (anti embolism stockings)
  • using compression devices (intermittent pneumatic compression)
  • seeing a physiotherapist to help you get out of bed and move around as soon as possible
  • stop taking certain drugs such as the combined oral contraceptive pill or hormone replacement tablets
  • having fluids so that you don't become dehydrated

Anti embolism stockings

You may be given anti embolism stockings to wear until you are moving around as usual. These are tight stockings that squeeze your feet and legs, helping the blood to circulate more quickly. Your nurse will measure your legs to make sure you have the right size. 

You cannot usually wear these stockings if you have:

  • fragile skin, eczema or recently had a skin graft
  • narrowing of the blood vessels leading to your legs (peripheral arterial disease)
  • swollen legs
  • recently had a stroke
  • tingling or numbness in your fingers or toes (peripheral neuropathy)

Intermittent pneumatic compression

Your doctor may suggest you use an intermittent pneumatic compression device. You wear this around your legs and feet. It inflates regularly to keep the blood circulating well. You use this while you are in bed or in a chair.

Going home

Your doctor or nurse will tell you if you need to wear stockings or take blood thinners at home. They will advise you how long to take treatment for and who to contact if there are any problems.

If you've had major surgery to your tummy (abdomen) or pelvis, you have injections of heparin for 4 weeks after your operation. You have them every day as an injection under the skin (subcutaneous injection). Your nurse will show you how to do it before you go home.

The video below shows you how to give a subcutaneous injection. The video is 3 minutes long.

Tips for preventing blood clots

Remember to:

  • take short walks as often as possible
  • keep active
  • do simple leg exercises like bending and straightening your toes every hour if you can't move around much
  • drink plenty of water
  • report any symptoms to your doctor or nurse straight away

Your feelings

The risk of developing a blood clot is higher in the first few months after being diagnosed with cancer. You might worry about how this complication will affect your cancer treatment.

It is important to understand that often blood clots are a normal part of the cancer journey. It’s normal to feel anxious about experiencing one.

Remember that doctors can successfully treat blood clots when diagnosed. This should not interfere with your cancer treatment. 

Who can help you?

For support and information, you can call the Cancer Research UK information nurses. They can give advice about who can help you and what kind of support is available. Freephone: 0808 800 4040 - Monday to Friday, 9am to 5pm.
  • Venous thromboembolism in over 16s: reducing the risk of hospital-acquired deep vein thrombosis or pulmonary embolism
    National Institute for Health and Care Excellence (NICE), 2019

  • Venous thromboembolism in adults
    National Institute for Health and Care Excellence (NICE), 2021

  • Management of venous thromboembolism (VTE) in cancer patients: ESMO Clinical Practice Guidelines
    M Mandala, A Falanga and F Roila
    Annals of Oncology, 2011. Vol 22, Supplement 6. Pages 85-92

  • Incidence of venous thromboembolism and its effect on survival among patients with common cancers
    H Chew and others
    JAMA Network, 2006. Vol 166, Issue 4. Pages 458-464

  • Cancer-associated thrombosis: an overview of mechanisms, risk factors and treatment
    N B A Razak and others
    Cancers (Basel), 2018. Vol 10, Issue 10. Page 380

  • The information on this page is based on literature searches and specialist checking. We used many references and there are too many to list here. Please contact with details of the particular issue you are interested in if you need additional references for this information.

Last reviewed: 
10 Feb 2022
Next review due: 
10 Aug 2026

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