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Causes of breathlessness

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This page has information about the causes of breathlessness. There is information about



Red blood cells are made in your bone marrow. They contain haemoglobin (Hb). This is what carries oxygen around your body. If the level of haemoglobin in your blood is low, you have anaemia. An important part of haemoglobin is iron. So your doctor may say you are low in iron if you are anaemic.

Anaemia makes you very tired and you may also become breathless because your blood is carrying less oxygen. Anaemia can be a side effect of cancer treatments such as chemotherapy and radiotherapy. Or your cancer itself can cause anaemia. If this is the cause of your breathlessness, treatment for your anaemia can help you to feel less breathless.


Side effects of treatment

Surgery, chemotherapy or radiotherapy can all cause breathing problems.

If you have had surgery to remove part of your lung, a lobe of a lung (lobectomy) or all of one of your lungs (pnemonectomy), this can affect how well you breathe.

If you are having surgery to remove a 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 health 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 problems afterwards.

A number of factors help your doctors decide which type of lung surgery is best for you and if you are fit enough to have surgery. You will have tests called lung function tests. Your specialist won't agree to remove a whole lung unless they are sure you can manage with just one.

Chemotherapy drugs such as bleomycin can cause inflammation of the lungs, and this can also cause breathlessness. This reaction is rare and only happens in about 1 in 10 patients treated with this drug. If you have a lot of bleomycin treatment, it can cause permanent breathlessness from scarring (fibrosis) in the lung. But doctors are very aware of this long term side effect and will make sure you don’t have too much of this drug.

Treatment with the immunotherapy drug interleukin 2 (IL2 or Aldesleukin) can sometimes make fluid leak out of the small blood vessels in your body. This can lower your blood pressure, cause swelling in your abdomen or lungs and cause breathing difficulties. It is important to let your doctor or nurse know right away if you have any shortness of breath when you are having treatment with interleukin 2. This side effect is very rare if you are having your IL2 as small injections under the skin. It only tends to happen when people have larger doses injected straight into the blood, and even then it is not very common.

The lungs are quite sensitive to radiation. But radiotherapy is a useful treatment for lung cancer. Radiotherapy to the chest can cause scarring or inflammation of your lung tissue. This can make breathing problems worse if you have lung cancer. You may notice that you are more breathless for a few weeks or months after finishing your radiotherapy, but there is treatment you can have for this.


Heart problems

Most heart problems that cause shortness of breath are not related to cancer. They are caused by other medical conditions such as congestive heart failure. But sometimes cancer or its treatment does cause heart problems that lead to breathlessness because

  • The tumour 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.

A chemotherapy drug called doxorubicin can cause temporary damage to the muscles of the heart. It may change the rhythm of the heartbeat. In most people this will go back to normal after you have finished your treatment. But with high doses or repeated treatments of doxorubicin there is a small risk of long term heart damage. Herceptin may also cause temporary damage to the heart muscle.


Chest infection

Sometimes people with cancer are more likely to pick up infections because the treatment they are having affects their bone marrow. This is where your white blood cells are made. White blood cells fight infection. So if you have too few, you are at increased risk of infection.

Having a chest infection will affect the way you breathe. If you have a serious infection, such as pneumonia, breathing will be even harder.

Coughing up phlegm and a raised temperature are signs that you may have a chest infection. Contact your GP if you are worried. You may need a course of antibiotics.

Remember – infections can sometimes be life threatening. You should contact your doctor urgently if you think you have an infection.


Fluid on the lungs or abdomen

It is quite common for fluid to collect when cancer affects the outer covering of the lungs. Two sheets of tissue called the pleura or pleural membranes cover the lungs. The fluid collects between them and is called a pleural effusion. When you breathe in, the lungs expand. When you have a pleural effusion, they can't expand as far because the fluid is taking up space that the lung would otherwise expand into. This will make you short of breath.

Diagram showing a build up of fluid in the lining of the lungs (pleural effusion)

Cancer can also make fluid build up in the abdomen. This fluid is called ascites. Ascites is quite common in women with cancer of the ovary. Cancer cells attach themselves to the lining of the abdomen and irritate it. This makes the abdominal lining make fluid, which collects in the abdomen. People with secondary liver cancer may also get ascites because of congestion in the liver making pressure build up in the circulation. The pressure makes fluid leak out from the bloodstream and lymphatic system and collect in the abdomen.

Diagram showing fluid in the abdomen (ascites)

If there is a lot of fluid, your abdomen can become quite swollen. So it pushes upwards, against your stomach and the sheet of muscle that separates your abdomen from your chest (the diaphragm). The increased pressure on your diaphragm makes it harder for your lungs to expand when you breathe in. This can make you breathless.

We have more detailed information about ascites.

If you have a pleural effusion or ascites, doctors can usually drain the fluid to make your breathing easier. But this does not usually cure the problem for good because the fluid is likely to build up again.

If your doctors talk about fluid on the lung they may mean pleural effusion. Or they may mean you have fluid actually collecting inside the lung. This is called pulmonary oedema. Unfortunately, it isn’t possible to have this type of fluid collection drained. Pulmonary oedema is most often due to heart problems so you need treatment for your heart to stop the fluid collecting.


Tumour growth

If you have a cancer in or near your lungs, it may put pressure on your airways, or start to block them. This may narrow the tubes that carry air into your lungs, making it difficult for the air to get through. This will make it difficult to breathe normally. If you have a blockage high up in your main airways, you may have a symptom called stridor. This is noisy breathing. You can actually hear the air going in and out, past the blockage.

Doctors can use laser treatment to cut away any tumour that is blocking a main airway and making breathing difficult. There is information about laser treatment in the section on treating breathing problems.


Blood vessel blockage

Breathlessness can be caused by a blockage in the large blood vessel in the neck called the superior vena cava. This symptom is known as superior vena cava obstruction (SVCO). It can be caused by 

  • A blood clot within the blood vessel
  • The tumour itself 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. It can also cause symptoms such as a swollen face, chest pain, cough, dizziness, and eyesight changes. SVCO can happen in lung cancer and sometimes in other cancers such as breast cancer, oesophageal cancer, and non Hodgkin lymphoma.

SVCO needs urgent treatment. You might need oxygen, and steroids to reduce the swelling in your neck. You might also have water tablets (diuretics) which make you pass more urine to help reduce swelling. The doctor may put a thin tube called a stent into the vein to keep it open. You may have radiotherapy or chemotherapy to try and shrink the tumour and stop it pressing on the vena cava. If SVCO is caused by a blood clot, you have drugs to thin the blood (anti coagulants), such as heparin and warfarin.


Other causes of breathlessness

If you are short of breath, it may not be due to cancer. There are many other medical conditions and circumstances that can make you feel breathless. These include

  • Lung diseases such as emphysema, chronic obstructive pulmonary disease (COPD, sometimes called COAD)
  • Asthma
  • Heart problems such as congestive cardiac failure (CCF)
  • Tobacco smoking
  • Being overweight
  • Blood clots
  • Being in a lot of pain
  • Anxiety and other emotional problems

The right treatment will depend on the cause. We can’t go into all the treatments for these conditions here. But do ask your doctor or nurse if you want to know more. They will be able to explain the cause and the thinking behind the treatment they’ve chosen for you. There is more information in the treating breathlessness section.

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Updated: 25 October 2014