Cancer and the risk of blood clots

When you have cancer you may be at more risk of developing blood clots. The medical name for these are a deep vein thrombosis (DVT) and pulmonary emboli (PE). Find out about more about DVTs and PEs, the symptoms and what treatment you might have.

What is DVT?

A blood clot can block the normal flow of blood. The medical name for a blood clot in the deep veins of the leg is a deep vein thrombosis (DVT).

Part or all of a deep vein thrombosis may 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. This happens in blood vessels called the pulmonary arteries. The medical name for these blood clots is a pulmonary embolism (PE). DVTs and PEs together are sometimes called venous thromboembolism (VTE).

In people who have cancer blood clots can also form in long lines or central lines such as a PICC line. These clots can also break off and form a pulmonary embolism. 

The veins normally carry blood around the body back to the heart. A blockage like this can cause a number of symptoms.

A blood clot can be very serious if it moves through your body because it will end up causing a blockage in the blood supply to your lungs.

Most clots when diagnosed can be successfully treated so it's important to report any symptoms to your doctor or nurse immediately.


The common symptoms of a blood clot are:

  • pain in the deep muscles of your leg that is unexplained
  • redness and swelling in your leg - this may be just in the calf or include the whole of your leg

If the clot has moved to your lungs (a pulmonary embolism or PE), the symptoms are: 

  • 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 light headed
Dial 999 if you have symptoms of a clot in your lung

Who is at risk?

Having cancer might mean that you have a higher risk of developing a blood clot. Around 15 out of 100 people with cancer develop a blood clot. There are a number of reasons why this is, they include: 

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

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

When chemotherapy kills cancer cells, the cells can also release substances that cause more blood clotting. 

Some chemotherapy drugs may cause this sticky blood more than others. Your doctor will explain if the drugs you are having increase this risk. 

The hormone drug tamoxifen is also known to increase the risk of blood clots. Doctors are very clear that the benefits of tamoxifen far outweigh the risks for women with breast cancer but you should be aware of the symptoms of a blood clot just in case.

Surgery and chemotherapy can both damage the walls of blood vessels. 

You are at a slightly higher risk of developing a blood clot if you have cancer of the pancreas, bowel, lung, stomach, ovary, or womb. Also, the risk is higher in cancers that have spread to nearby lymph nodes or other parts of the body.

Sometimes your cancer or treatment can make you feel very ill. You could 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 surgery you may not be able to move around much at first and the team caring for you may 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 increase the risk of clots.

Taking the oral contraceptive pill or hormone replacement therapy (HRT) will increase the risk of developing a blood clot. 

Other medical conditions such as diabetes or heart disease, can also make the blood more sticky and increase the risk.

Doctors will also treat any underlying causes which often resolves the problem.

Your feelings

Over half of blood clots occur within the first three months of being diagnosed with cancer. To experience what is often described as a complication so early may be distressing for some people.

It is important to understand that blood clots are a normal part of the cancer journey and it is not unusual to feel anxious about experiencing one. However, blood clots are readily treatable and should not interfere with your cancer treatment. 

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. The most common types of anticoagulants are:

Low molecular weight heparins such as dalteparin, enoxaparin and tinzaparin

You have low molecular weight heparins as an injection just under the skin (subcutaneously). You may need regular blood tests. These injections are the most common treatment for new blood clots in people with cancer.

Unfractionated heparin

Heparin works immediately when you have it 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.

You will have regular blood tests to check the amount of heparin in your blood. If you have heparin into your vein as an infusion you will need to stay in hospital for a few days.


Warfarin comes as a tablet and doctors most often prescribe it to people who have a heart condition called atrial fibrillation. This causes an irregular and fast heart rate.

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

Direct oral anticoagulants (DOACs)

These include apixban, dabigatran, edoxaban and rivaroxaban.

They are a new type of blood thinners that mean you don't need to have regular blood tests. They are used to prevent stroke in people with atrial fibrillation and as a treatment with blood clots in people who don't have cancer. There is a risk of bleeding with some types of cancer.

Researchers are looking into whether they are better or as good as other types of treatment for blood clots for people with cancer. 

Reducing the risk of DVT while in hospital

The National Institute of Health and Care Excellence (NICE) has produced guidance about reducing the risk of DVT for patients in hospital.

Before an operation your doctor will assess your risk of developing blood clots. They may advise you to stop taking particular medicines for a week or so before your surgery.

Treatment to reduce your risk

Your doctor will suggest you have preventative treatment to reduce your risk of developing a blood clot if you are at higher risk. You will have small doses of a blood thinner. You can also reduce your risk by drinking plenty of water or soft drinks and by keeping active. Your nurses and physiotherapists will get you out of bed and moving around as soon as possible.

Before surgery your doctor may advise you to stop taking the combined oral contraceptive pill or hormone replacement tablets before your surgery. You will be given fluids so that you don't become dehydrated after your operation. Your nurses and physiotherapists will get you out of bed and moving around as soon as possible.

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 first of all 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)

You may be offered treatment with an intermittent pneumatic compression device. You wear this around your legs or feet and it inflates regularly to keep the blood circulating well. You will be encouraged to use this while you are in bed or in a chair.

Your doctor may give you blood thinning drugs to help prevent blood clots. Depending on the type of surgery you have, you may have this as a daily injection of a low molecular weight heparin or fondaparinux, or after hip or knee replacement as a tablet. 

Your medical team will tell you if you need to wear your stockings or take anticoagulant at home. They will advise you how long to take your treatment for and who to contact if there are any problems.

If you've had major surgery to your abdomen or pelvis, you will continue having daily injections just below your skin for 4 weeks after your operation.

Tips for preventing DVT

Remember to:

  • take short walks as often as possible
  • 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
Last reviewed: 
21 Nov 2018
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  • Management of venous thromboembolism in patients with cancer.
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    J Thromb Haemost. 2011 Jul;9 Suppl 1:316-24. 

  • Venous thromboembolism and prognosis in cancer.
    AA Khorana
    Thromb Res. 2010 Jun;125(6):490-3. 

  • Psychological impact of cancer associated thrombosis 
    Seaman S, Nelson A, Noble S. 
    Patient Preference and Adherence 2014;453–61.

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