There are a number of possible causes of breathlessness. Your doctor will be able to tell you the cause of your breathlessness so that you can get the most helpful treatment. In this section, we describe common causes, including the effect of some cancer treatments.
Cancer affecting the lungs
This can be a primary lung cancer (cancer that started in the lungs) or a secondary cancer that has spread to the lung from another part of the body. Treatments such as radiotherapy or chemotherapy may help shrink the tumour and relieve any breathlessness caused by the cancer. We can send you information about the type of cancer you have and its treatments.
A build-up of fluid in the lining of the lungs (pleural effusion) or stomach (ascites)
If cancer cells irritate the lining of the lungs or stomach, this can cause a build-up of fluid. This means there is less room for the lungs to expand. Pleural effusion and ascites can be treated by removing (draining) the fluid.
Low levels of red blood cells in the blood (anaemia)
This can be due to the cancer or its treatment, including chemotherapy and radiotherapy. Red blood cells carry oxygen around the body. If the level of red blood cells in your blood is low, you may become very tired and breathless.
Your doctors may recommend that you have a blood transfusion.
These cause phlegm in the airways and can make you feel breathless. It’s important to drink a good amount of fluid to dilute the phlegm so you can cough it up more easily. If you develop a raised temperature (above 38°C or 100.4°F), a chesty cough or pain when you breathe, contact your doctor immediately as you may need antibiotics.
In advanced cancer, the muscles that help breathing can become weak because of reduced physical activity, fatigue, lack of nutrition and weight loss. This can make breathing more difficult.
Pain that’s poorly controlled can make it difficult to breathe and move comfortably. Tell your doctor about any pain you’re experiencing so they can make sure it’s being managed.
A blood clot in the lung (pulmonary embolism)
This can cause sudden breathlessness and pain when you breathe. If you have these symptoms, contact your doctor immediately.
Some other conditions can cause breathlessness, such as congestive heart failure, asthma, chronic obstructive pulmonary disease (COPD) and pulmonary oedema (a build-up of fluid in the lungs). Your doctor can advise you on the treatment you need.
Smoking makes breathlessness worse. The smoke causes irritation and inflammation of the airways. As a result, less oxygen gets absorbed into the bloodstream. If you want to stop smoking, ask your nurse or doctor about help that’s available locally, such as free local NHS Stop Smoking Services. You can also call our cancer support specialists for more advice.
Anxiety and panic
Feelings of anxiety and panic are common. They’re natural reactions following a cancer diagnosis and during treatment. However, they can cause some people to have rapid and shallow breathing. Becoming breathless can itself cause further anxiety and panic.
Surgery for lung cancer may remove part, or all, of a lung. Many people are able to breathe well after they recover from surgery, but some people do experience breathing problems.
Radiotherapy to the chest can cause inflammation of the lung (pnuemonitis), which can lead to breathlessness. This is usually a short-term problem, but some people can have it in the long-term. Sometimes, people who have intensive radiotherapy to the chest can develop hardening and thickening (scarring) of the lung, which can cause long-term breathlessness.
Chemotherapy drugs can also sometimes cause breathing problems.
Your cancer specialist can tell you about any effects your treatment may have on your breathing and answer any questions you have. If you experience breathlessness, always let your doctor know.