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 are. You may hear them say:

• deep vein thrombosis (DVT)

• pulmonary embolism (PE)

• venous thromboembolism (VTE)

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

Surgery and other cancer treatments can increase the risk of developing blood clots. This includes the cancer drugs:

• cisplatin

• tamoxifen

• L-asparaginase

• thalidomide

• lenalidomide (Revlimid)

• bevacizumab (Avastin)

Find out more about different cancer drugs from our A to Z list

You may have some cancer drugs into your bloodstream (intravenously). Sometimes this is through a long plastic tube that goes into a large vein in your chest. These include central lines and PICC lines. They 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. Blood clots can also form in these lines.

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.

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 veins depend on them being squeezed by your muscles when you move. Immobility reduces the blood flow in the body and blood can stagnate in the legs and arms and become sticky.

Moving around helps reduce the risk of clots. Even doing leg exercises such as moving your feet up and down in bed or in the chair can help. Especially if you don’t feel well enough to walk around.

After cancer surgery, you may not be able to move around as much as you normally would. Your nurse 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. Speak to your doctor or pharmacist if you are planning a long journey. They will talk to you about ways to reduce the risk.

Other factors

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

• having a blood clot in the past

• taking the oral contraceptive pill or hormone replacement therapy (HRT)

• certain medical conditions such as diabetes or heart disease

• being overweight

• having varicose veins – these are veins that are swollen and lumpy under the skin

• having an inflammatory condition such as Crohn's disease or rheumatoid arthritis

• not having enough fluid in your body (dehydration)

Smoking can also increase the risk of a blood clot. If you would like to stop smoking there are a range of support services and different products to help you.

Read more about how you can stop smoking

Tests for blood clots

If your doctor thinks you might have a DVT, they ask you to have some tests. This can include:

• blood tests

• an ​ultrasound​ scan of the arm or leg

If they want to check whether you have a PE, they may ask you to have tests including:

• a scan to look at your lungs – doctors call this a computed tomography pulmonary angiogram (CTPA)

• an ​echo​ (echocardiogram)

• ​ECG​ (electrocardiogram)

Sometimes your doctor may want you to have other tests. They will explain what the tests are for and how to prepare for them.

Find out more about these tests and scans from our A to Z list

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 blood clots are a common complication if you have cancer. 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?