Causes of breathlessness in people with cancer

There are many reasons why you might get breathless when you have cancer. It can be caused by the cancer or its treatment. Other medical conditions can also cause breathlessness. 

Causes of breathlessness include:

  • the cancer itself
  • side effects of cancer treatment
  • fluid on the lungs (pleural effusion)
  • fluid in the tummy (ascites)
  • heart problems
  • blood vessel blockage in the neck
  • infections
  • a low number of red blood cells (anaemia)
  • blood clots

Contact your 24 hour advice line if you notice any changes in your breathing. If you can't speak to someone quickly, call 999 or go to your local Accident and Emergency (A&E). You may need urgent treatment.

Breathlessness caused by cancer

You can feel breathless if you have cancer in or near your lungs. This includes cancer that has spread to the lungs from other parts of the body (advanced cancer). 

Cancer near the lungs can also put pressure on your airways Open a glossary item . This might narrow or block the tubes carrying air into your lungs, making it difficult for air to come through. This makes it difficult to breathe normally. 

A blockage in the upper airways can cause noisy breathing. This is called stridor. You might be able to hear the air going in and out past the blockage.

Breathlessness caused by side effects of cancer treatment


Surgery to remove part of your lung, a lobe of your lung, or one of your lungs, can affect how well you breathe.

If you are having surgery on the lung, you may worry that you will have a lot of difficulty breathing after the operation. This is not always the case.

Depending on the volume of the lung you have left, you may still be able to breathe quite normally. If you were short of breath before your operation, you may still have some breathing problems afterwards.

Your doctor considers a number of factors before they decide which type of lung surgery is best for you and if you are fit enough to have surgery. 

Breathlessness caused by cancer drugs  

The side effects of some anti cancer drugs can cause breathlessness, this might be due to:

  • inflammation and scarring of the lungs
  • an allergic reaction causing you to become suddenly short of breath
  • an infection due to a low level of white blood cells

Your healthcare team are aware of the side effect of the drugs you have. They will explain the risk of becoming breathless and check you regularly for any problems.

It is important to let your doctor or nurse know straight away if you have any breathing problems during or after your treatment. 

Drug treatments that may cause breathlessness include:

  • bleomycin - a chemotherapy drug
  • interleukin 2 – an immunotherapy drug
  • cabozantinib – a targeted cancer drug


Having radiotherapy to the chest can cause:

  • shortness of breath
  • inflammation of the lung (pneumonitis)

These side effects can start during your treatment and often also continue afterwards. They will usually improve a few weeks after your treatment finishes. But they can be a long term problem for some.

Fluid build up in the lungs (pleural effusion)

When cancer affects the lungs, fluid can sometimes collect between the sheets of tissue that cover the outside of the lung and the lining of the chest cavity. These sheets of tissue are called the pleura. Doctors call this fluid collection a pleural effusion. 

The fluid stops your lungs from expanding fully. So you have to take shallower breaths and make more effort to breathe. 

Fluid build up in the tummy (ascites)

Some advanced cancers can cause fluid to build up in the tummy (abdomen). This is called ascites. This fluid can cause pressure on the diaphragm Open a glossary item. This then puts pressure on the lungs and causes breathlessness. 

Heart problems and breathlessness

Most heart problems that cause breathlessness are not related to cancer. They are often caused by other medical conditions such as congestive heart failure. But sometimes cancer or its treatment does cause heart problems that lead to breathlessness. This might be because:

  • the cancer is putting pressure on your heart
  • side effects from treatments such as chemotherapy or radiotherapy may affect your heart

Some types of cancer can grow very near the tissue that surrounds and protects your heart (the pericardium). This can interfere with how much blood the heart can pump out and may make you short of breath.

Some cancer medicines can affect the heart, which may then lead to breathing problems. Your doctor will let you know if any of the drugs you are taking might cause heart problems. You have regular tests during your treatment to check how well your heart is working if:

  • your cancer medicines are known to affect the heart or
  • you have any symptoms 

There is a chance that a small part of the heart might be in the radiotherapy treatment area if you have radiotherapy to the left side of the chest. This is less common now as newer radiotherapy techniques are available. 

The heart is sensitive to radiation. Another side effect of having radiotherapy near the heart is a build-up of fluid around the heart (pericardial effusion). This can cause breathlessness. If this happens, you may need a procedure to drain the fluid.

Breathlessness caused by blood vessel blockage 

There is a large blood vessel in the neck called the superior vena cava. This vessel might become blocked. This is called superior vena cava obstruction (SVCO). The most common symptom is shortness of breath. 

It can happen in different cancers including:

  • lung cancer
  • breast cancer
  • non-Hodgkin lymphoma

Causes of blood vessel blockage

Blockage of the blood vessel (SVCO) can be caused by:

  • a blood clot within the blood vessel
  • the cancer pressing on the blood vessel
  • cancer in the nearby lymph nodes, making them larger and pressing on the blood vessel

The pressure on the blood vessel stops blood going back to the heart from the head and arms. This causes swelling around your windpipe (trachea) making breathing difficult.


Symptoms of blood vessel blockage in the neck include:

  • swelling of the face, larynx (voice box), neck, and arms
  • chest pain
  • a cough
  • dizziness
  • eyesight changes
  • headache

Call your hospital 24 hour advice line straight away if you have any of these symptoms.


You need urgent treatment for SVCO. You will have oxygen and medicines to reduce the swelling and relieve other symptoms. You may have a thin tube called a stent put into the vein to keep it open. Some people have radiotherapy or chemotherapy to try and shrink the cancer and stop it pressing on the superior vena cava. 


Your bone marrow Open a glossary item makes white blood cells Open a glossary item. These cells are part of your immune system and help your body to fight infection. 

Cancer cells and cancer treatment can damage your bone marrow. If you don't have enough white blood cells, you have a higher risk of getting an infection. 

Some infections and in particular a chest infection will affect the way you breathe. If you have a serious infection, such as pneumonia, breathing will be even harder. 

Infection during cancer treatment can be very serious and can be life threatening. Contact your doctor or hospital advice line immediately if you have a raised temperature or other signs of infection. 


Red blood cells are made in your bone marrow. They contain haemoglobin (Hb) which carries oxygen around your body. When the level of haemoglobin in your blood is low, you have anaemia.

Anaemia makes you very tired. And you may also become breathless because your blood is carrying less oxygen.

Blood clots

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).

Feeling breathless is a common symptom if you have a PE. This might start suddenly or increase over time.

Blood clots can be very serious. Contact your hospital advice line straight away or call NHS 111 if you think you have a blood clot.

Anxiety and panic attacks

You may have shortness of breath when you are very anxious or get panicky. It might help to try breathing and relaxation techniques. These can help you feel more in control of your breathing.

Other possible causes of breathlessness

Other medical conditions can cause breathlessness, these include:

  • chest pain - call 999 for urgent attention if you have this
  • lung diseases such as emphysema, chronic obstructive pulmonary disease (COPD)
  • asthma
  • pain
  • a collapsed lung
  • Management of dyspnea in palliative care

    A.M. Crombeen and E.J. Lilly

    Current Oncology, 2020. Volume 27, Issue 3, Pages 142–145.

  • Malignant Venous Obstruction: Superior Vena Cava Syndrome and Beyond

    T Friedman and others

    Seminars in Interventional Radiology, 2017. Volume 4, Issue 4, Pages 398–408.

  • Palliative Care and the Management of Common Distressing Symptoms in Advanced Cancer: Pain, Breathlessness, Nausea and Vomiting, and Fatigue

    L. Henson and others

    Journal of Clinical Oncology, 2020. Volume 38, Issue 9, Page 905–914.

  • Dyspnea in Patients Receiving Radical Radiotherapy for Non-Small Cell Lung Cancer: A Prospective Study

    Angela Sardaro and others

    Frontiers in Oncology, 2020. Volume 10.

  • Palliative procedures in lung cancer

    E Masuda and others 2013

    Seminars in interventional radiology, 2013, Volume 30, Issue 2, Pages 199-205.

  • 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: 
05 Sep 2023
Next review due: 
05 Sep 2026

Related links