What Is a Malignant Pleural Effusion?


Pleural effusion is the term used to describe the accumulation of fluid within the space between the chest and the lungs, known as the pleural space.1 Pleural effusion becomes malignant when cancer spreads to the pleural space and continues to grow within the region. Malignant pleural effusion (MPE) is often used as a confirmation that cancer from another part of the body has metastasised (spread) to the lungs and potentially other regions of the body.1 MPE essentially is the accumulation of fluid and cancer cells within the pleural space.2 Pleural effusion should not be confused with pulmonary oedema (a condition in which fluid accumulates within the lung

Pleural effusion

Pleural effusion is a medical condition in which excessive fluid accumulates within the pleura of the lungs. It is also commonly known as “water in the lungs” due to the chest discomfort commonly felt in patients with the condition.3 Lung pleura is the tissue lining the lungs and chest wall; lung pleura functions to lubricate the lungs and chest wall to allow breathing.3 Usually, there is a small amount of fluid present within the pleura to lubricate the lungs for breathing.3 MPE may be caused by the combination of cancer and its complications, while pleural effusion can be caused by a variety of non-cancerous conditions.4 Pleural effusion differs from MPE in that pleural effusion is the accumulation of fluid without the additional presence of cancer cells in the pleural space. 


Pleural effusion symptoms vary from patient to patient: some patients do not experience any symptoms, while others may experience very severe symptoms.3 Also, in some cases, a patient’s symptoms may not be attributed to the pleural effusion itself but rather to the primary condition that is causing the pleural effusion.3 Symptoms of pleural effusion are as follows:

  • Chest pain: Chest pain is a very common symptom of pleural effusion as it often arises from the complications of excess fluid within the pleural space. Chest pain arises due to the pleural tissue’s inflammatory response to the excess fluid.4 This response causes pain and inflammation within the lung and chest area.4 
  • Dyspnoea: Dyspnoea, commonly known as shortness of breath, is the most common symptom of pleural effusion.4 It directly results from the effects of the excessive fluid within the pleural space. Dyspnoea’s severity has a direct correlation to the size (amount of excessive fluid in the pleural space) of pleural effusion; the excessive fluid can disrupt and alter the function of lung parenchyma (area of the lungs involved in gas exchange for breathing).4 Shortness of breath may occur at rest or during physical activity.2  
  • Dry cough: Dry cough is reported by some patients as a symptom of pleural effusion. It often results from the pleural tissue’s inflammatory response to excessive fluid.4 Dry cough may also result from lung compression due to the presence of abnormal fluid.4 
  • Fatigue: Fatigue may also be a symptom of pleural effusion due to the increased strain on the chest and lungs that the excessive fluid causes.2, 4 Fatigue can be brought about by the increased energy needed for the lungs to perform breathing as a result of the fluid.2
  • Discomfort when lying flat: Patients with pleural effusion may experience discomfort when lying flat as a result of the increased pressure that the excess fluid places on the lungs and chest wall.1 This can also lead to sleep difficulties and other complications. 

Additional symptoms also include the inability to exercise, general sickness and pain during deep breathing.1-3 In severe cases of the condition, patients may have up to four litres of excess fluid within the pleural cavity.5  

Causes and risk factors

MPE is a form of pleural effusion that is caused by the presence and spread of cancer from one organ system to the pleural space.1 According to Cancer.net, approximately 40% of patients with lung cancer experience pleural effusion along the course of their cancer.1 Other types of cancer that commonly cause pleural effusions include breast cancer, lymphoma (cancer of the lymph system), mesothelioma (a form of lung cancer that results from long-term exposure to asbestos fibres) and ovarian cancer.1 Pleural effusion is also a sign of further spread and development of cancer to the lymph nodes, which can also result from cancer treatments such as radiation therapy, surgical removal of a tumour, chemotherapy and anti-cancer drugs.1  

There are also non-cancer-related causes of pleural effusion. In these cases, the excess fluid can be either protein-rich or water-rich, depending on the cause of the effusion.3  

Water-rich pleural effusion can manifest from complications within the cardiovascular and respiratory systems, such as heart failure. Heart failure occurs when the heart is unable to pump blood around the body to sufficiently meet the body’s blood and nutrient requirements.6 This can result in the accumulation of blood and its associated fluids in other parts of the body, especially the lungs. As a result, patients with heart failure are at an increased risk of pleural effusion. Pulmonary embolism is another potential cause of pleural effusion; it occurs when a blood clot gets trapped in the blood vessels of the lungs.7 This causes the accumulation of fluid in the pleural space as a result of the increased pressure from the blood clot.

On the other hand, pneumonia and kidney disease can cause protein-rich pleural effusions. Pneumonia is a lung condition in which the lung is infected by bacteria or a virus, resulting in inflammation of the airways and the alveoli (air sacs of the lung) filling with mucus.9 This mucus can also spread to the pleural space, leading to pleural effusion. Kidney disease is when there is reduced functioning of the kidney resulting in an increase of fluid within the body and high blood pressure.3 As the kidneys filter the blood and aid in the production of urine, when they do not properly function, toxins accumulate in the blood and excess minerals and water are not excreted as urine. The excessive fluid from the decreased function of the kidney may settle within the pleural space, causing pleural effusion.

Other less common causes of pleural effusion include tuberculosis, autoimmune conditions, abdominal infections, internal bleeding (especially following trauma to the chest), chylothorax (accumulation of lymph fluid within the chest), poor nutrition, respiratory failure and exposure to asbestos fibres.1,3 

There are several risk factors for pleural effusion. Many of these risk factors are also common cancer risk factors, as pleural effusions are most commonly a direct result of some forms of cancer. Risk factors include: 

  • Heart Failure: Improper function of the heart can lead up to the buildup of blood and other fluids in the pleural space and other parts of the body.6,10
  • Connective Tissue Disorders: The pleural tissue itself is connective tissue, so any abnormalities in the pleural tissue can increase one’s susceptibility to pleural effusion.10
  • Chest Injuries: Chest injuries can cause internal bleeding, which can lead to the accumulation of blood in the pleural space. Chest injuries can also lead to lymph fluid accumulation within the pleural space, known as chylothorax.1,3,10 
  • Surgery: Surgeries of the heart, abdominal region, and lungs and also organ transplants, are the most notable risk factors.10 This may be due to the increased risk of infection during and following surgery. Infections of the heart, abdomen and lungs can lead to inflammation and eventually fluid buildup in the interstitial space.11 
  • Pre-existing Lung Disease: Patients that have pre-existing lung conditions are at increased risk of pleural effusion due to the fragility of the lung tissue.11 
  • Family History of Cancer: As cancer is one of the most common causes of pleural effusions, having a family history of cancer indirectly increases one’s risk of suffering from a pleural effusion.1
  • Ascites: Ascites are conditions in which fluid builds up in the abdomen. The fluid in the abdomen can spread to the lungs and other organs. If the fluid reaches the lungs, it may sequester itself in the pleural space, resulting in the occurrence of a pleural effusion.12  
  • Use of certain drugs: Certain drugs can directly cause pleural effusion through their mechanism of action.3 Examples include nitrofurantoin (used to treat urinary tract infections), dantrolene (used to treat muscular disorders) and amiodarone (used in the prevention and treatment of arrhythmias of the heart’s ventricles).3 
  • Asbestos Fibre Exposure: Long-term exposure to asbestos can cause mesothelioma, a cancer form that causes cancer cells to grow and develop on the tissues lining the heart, lungs and abdomen,3 which can increase one’s risk of developing an MPE.3 

There are several causes and risk factors of pleural effusion that affect both the type of fluid that accumulates within the pleural space and the overall classification of the pleural effusion. These causes and risk factors can also affect the severity and treatment methods of pleural effusions. 

Malignant pleural effusion 

MPE and cancer

MPEs are pleural effusions that result from complications of certain forms of cancer.3 They occur when both excessive fluid and cancerous cells accumulate within the pleural space, leading to several complications.2 They cause several serious symptoms such as breathing difficulties, chest pain, weight loss, muscle wasting and difficulties performing everyday activities.12 MPEs are also considered an indicator of a poor cancer prognosis. It is estimated that in the United Kingdom 50,000 new diagnoses of MPE occur annually. The most common cause of MPE is lung cancer followed by breast cancer.3 Lung cancer and breast cancer account for up to 65% of cases of the condition.12  

Studies have shown that cancer cells reach the lungs to reach the pleural space by travelling through the bloodstream to invade the pleural tissue.12 From then on, the cancer cells settle within the pleural tissue and continue to grow. It is currently being researched whether the nutrients and other substances in excessive pleural fluid support growth and spread.12 However, it is unknown why certain cancer forms (lung, breast, lymphomas and ovarian) can cause the development of pleural effusions but other forms do not. As multiple mechanisms ultimately cause the development of MPEs, the origin of the condition is largely dependent on the type of cancer that it originates from.12, 13 For example, as the breast and lungs are in close proximity to the pleural space, breast and lung cancer cells can directly invade the pleural space.13 In the case of ovarian cancer and certain lymphomas, cancer cells of these cancer forms can reach the pleural space via the bloodstream.13

Several conditions, like tuberculosis and benign asbestos pleural effusion, have a similar clinical presentation as MPE.13 Tuberculosis is the most common condition that is mistaken for MPE due to the similarities in symptoms between the two conditions.13 Benign asbestos pleural effusion is only considered for patients who have had long-term exposure to asbestos fibres. However, compared to patients with mesothelioma, patients with benign asbestos pleural effusion have smaller effusions and occur shortly following asbestos exposure.13 


Treatment options for pleural effusions ultimately depend on the type of pleural effusion (malignant or non-malignant). 

If a patient has an MPE, the cancer form that is causing the condition must be considered ​​when treating the condition.3 Cancer treatments such as radiotherapy, chemotherapy and anticancer drugs actually increase one’s risk for pleural effusions.1-3 Therefore, medical professionals must consider how to treat the patient’s MPE without impeding the treatment of underlying cancer. MPE cannot be left untreated as it further compromises the comfort of patients with cancer as they are being treated.1 

If a patient has a non-MPE, treatment must consider the condition or risk factor(s) that caused the pleural effusion. For example, if a pleural effusion is caused by heart failure, heart failure treatment drugs such as diuretics may be used to treat the pleural effusion.3 In most cases of non-malignant pleural effusions, the combination of treatment of the underlying condition causing the pleural effusion and directly treating the effusion itself is used.3 


Thoracentesis is a non-invasive medical procedure that doubles as a diagnostic and treatment method for pleural effusions.14 It is also used to decrease the pressure within the lungs, treat common respiratory disease symptoms of breathing difficulties and chest pain, and determine the cause of excessive fluid accumulation within the pleural space.14  

Before undergoing the procedure, your doctor will test your kidney function and determine if your blood makes blood clots normally.14 This step can rule out the conditions of kidney disease and pulmonary embolism. One should not undergo a thoracentesis if you are pregnant or allergic to any anaesthetics. You should also not take any blood thinning medications before undergoing the procedure.14

Thoracentesis is performed using either an X-ray machine, CT scanner or ultrasound equipment to aid in the guidance of a fine needle into the fluid within the pleural space.14 Patients are first placed under either general or local anaesthesia in the chest area. The needle is inserted in the skin between two ribs of the back. Once the needle reaches the pleural space, the doctor can begin the removal of the excessive pleural fluid through the use of a syringe or other suction instruments.14 Patients have often experienced the urge to cough due to the re-expansion of the lungs and/or a pulling sensation within the chest as the excess fluid is removed.14 

Tube thoracostomy

Tube thoracostomy is another minimally invasive treatment method that involves the insertion of a thin tube into the pleural space to remove the excess pleural fluid.15 Tube thoracostomy can be performed in two ways: a tube may be attached to a suction instrument to remove the excess fluid, or a tube is placed in the pleural space to deliver medications that reduce the chance of the accumulation of excess fluid.15 

Before undergoing a tube thoracostomy procedure, you must inform your doctor on the types of medications you are using or any allergies you may have if you want to be given anaesthetics before the procedure. Pregnant women should not undergo tube thoracostomy, as the radiation from the imaging equipment can be harmful to a developing baby.15 

Like thoracentesis, doctors may use a CT scanner, ultrasound imaging or X-ray imaging to help them guide the tube into the pleural space.15 A doctor or nurse will connect you to machines to monitor your heart rate, blood pressure and breathing rates over the course of the procedure.15 A small incision will be made at the site, and the tube is then placed. The tube is held still until imaging of the area, and the excess fluid is picked up by imaging technology. The excess fluid is then drained, allowing for full re-expansion of the lungs.15 As the lungs begin to re-expand, the medical team may instruct you to take deep breaths to aid lung expansion. 

Following the procedure, you may have to stay in the hospital until the chest tube is ready to be removed, or you may return home with the chest tube in place along with a portable draining system.15 Patients who go home with the chest tube will be provided with instructions on how to use and care over the chest tube and portable draining system.15 You may also be prescribed antibiotics and pain medications to reduce the risk of bacterial infection following the placement of the chest tube. 


A catheter is a treatment option for non-MPEs. It involves the insertion of a small tube into the pleural space to drain the excess fluid in a similar manner to tube thoracostomy and thoracentesis.16 

The insertion of a catheter is performed by a radiologist. Radiologists aim to select a location for catheter insertion that will drain the excess fluid successfully.16 Following the administration of anaesthesia, a small needle is guided into the pleural space via the aid of imaging technology. The doctor will make two small incisions: the needle will be inserted into one of these incisions (to enter the pleural space), while the catheter is placed in the other.16 The catheter also enters the pleural space. Your doctor will then secure the placement of the catheter by applying a dressing.16 Correct positioning of the catheter is checked via imaging technology. 

Insertion of a catheter allows patients to be able to drain recurring excess fluid at home, making this method suitable for patients suffering from MPEs.3,16 Patients with MPEs can suffer from recurrent pleural effusions due to underlying cancer of the condition. Catheter placement allows pleural effusion patients to be able to perform everyday activities without the associated uncomfortable symptoms.16 Catheter placement is also a low-risk procedure; however, potential risks include infection, exposure to X-rays and bleeding.16 


A shunt is used to treat pleural effusions by diverting the excess pleural fluid from the pleural space to another region of the body.1 For this fluid diversion to occur, a doctor must place a shunt into the affected area through surgical methods.1 Shunts are rarely used as a treatment method due to the increased risk of complications.1 A pleuroperitoneal shunt is commonly used to treat pleural effusions.14 Like catheter insertion, the insertion of a shunt is typically performed by a radiologist. Shunts must be placed via thoracoscopy (a medical procedure in which the inside of the chest is examined). The placement of a shunt allows the excess pleural fluid to be diverted to the peritoneal cavity (the area of the digestive system that contains the stomach, liver and intestines) of the abdominal area.14 The use of shunts is quite controversial due to their increased risk of infection and the potential for blockages to occur.14 The efficacy of shunts is also not agreed upon by medical experts contributing to their rarity as a pleural effusion treatment method.14 


Chemotherapy is quite varied as it is also an identified risk factor for the occurrence of pleural effusion. It is used as a treatment method in MPEs to treat the underlying cancer that is causing the condition.1 Immunotherapy, another cancer treatment method, is also used to treat MPEs.14 Treating cancer rather than the pleural effusion itself indirectly treats the condition due to the fact that MPEs occur due to the accumulation of cancer cells and pleural fluid within the pleural space.1 Therefore, if the underlying condition is managed, the occurrence of pleural effusions will eventually stop.1 It is important to note that chemotherapy will not clear out the excess fluid within the pleural space; it is used to kill the cancer cells within the area. 

For most patients with MPE, chemotherapy is not prioritised as a treatment method over standard treatment methods.14 However, due to the advancements in cancer treatment in the past few decades, researchers are trying to use chemotherapy to directly treat MPEs rather than just alleviate the symptoms.14 


The pleural space is an area between the lungs and the walls of the chest, and it typically contains a small amount of fluid to lubricate the lungs to perform breathing.1 However, excess fluid within the pleural space causes several adverse effects. Pleural effusion can be categorised into two types: malignant and non-malignant. MPEs occur when there is the presence of cancer cells and excess fluid within the pleural space.1 Non-MPEs may occur due to other conditions, such as heart failure, pulmonary embolism and kidney failure.3 

Pleural effusion can cause several symptoms such as chest pain, breathing difficulties, sleep problems and fatigue.4 They are most commonly caused by cancer and conditions of the cardiovascular, respiratory and digestive systems.4 

Treatment options for pleural effusions ultimately depend on the underlying cause of the condition. There are several procedures that patients may undergo to remove the excess fluid, such as thoracentesis, tube thoracostomy, shunts and the insertion of a catheter.14, 15 In MPEs, chemotherapy can be used to treat the underlying cancer.1,14 

Pleural effusion is a serious medical condition, and if you suspect that you may have a pleural effusion, contact a medical professional immediately. 


  1. Cancer.Net. Fluid Around the Lungs or Malignant Pleural Effusion [internet]. 2021 September [cited 2022 August 20]. Available from: https://www.cancer.net/coping-with-cancer/physical-emotional-and-social-effects-cancer/managing-physical-side-effects/fluid-around-lungs-or-malignant-pleural-effusion
  2. American Thoracic Society. Malignant Pleural Effusion [internet]. 2022 [cited 2022 August 20]. Available from: https://www.thoracic.org/patients/patient-resources/resources/malignant-pleural-effusions.pdf
  3. Cleveland Clinic. Pleural Effusion Causes, Signs & Treatment [internet]. 2018 December 18 [cited 2022 August 20]. Available from: https://my.clevelandclinic.org/health/diseases/17373-pleural-effusion-causes-signs--treatment#management-and-treatment
  4. Jany B, Welte T. Pleural Effusion in Adults- Etiology, Diagnosis, and Treatment. Deutsches Ärzteblatt International [internet]. 2019 May 24 [cited 2022 August 20]. Available from: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6647819/
  5. Yale Medicine. Fluid Around the Lungs (Pleural Effusion) [internet]. 2022 [cited 2022 August 20]. Available from: https://www.yalemedicine.org/conditions/fluid-around-the-lungs
  6. Cleveland Clinic. Heart Failure [internet]. 2022 January 21 [cited 2022 August 20]. Available from: https://my.clevelandclinic.org/health/diseases/17069-heart-failure-understanding-heart-failure
  7. Cleveland Clinic. Pulmonary Embolism [internet]. 2019 February 26 [cited 2022 August 20]. Available from: https://my.clevelandclinic.org/health/diseases/17400-pulmonary-embolism
  8. Light R. Pleural Effusion due to pulmonary emboli. Current Opinion in Pulmonary Medicine [internet]. 2001 July [cited 2022 August 20]. Available from: https://journals.lww.com/co-pulmonarymedicine/Abstract/2001/07000/Pleural_effusion_due_to_pulmonary_emboli.6.aspx#:~:text=The%20mechanism%20of%20pleural%20effusion,effusion%20have%20pleuritic%20chest%20pain.
  9. Cleveland Clinic. Pneumonia [internet]. 2020 June 15 [cited 2022 August 20]. Available from: https://my.clevelandclinic.org/health/diseases/4471-pneumonia
  10. Health Engine. Pleural Effusion [internet]. 2003 May 23 [cited 2022 August 20]. Available from: https://healthinfo.healthengine.com.au/pleural-effusion-3#Risk_Factors
  11. Beth Israel Lahey Health Winchester Hospital. Pleural Effusion [internet]. 2021 April 23 [cited 2022 August 20]. Available from: https://www.winchesterhospital.org/health-library/article?id=11619
  12. Psallidas I, Kalomenidis I, Porcel J, Robinson B, Stathopoulos G. Malignant Pleural Effusion: From Bench to Bedside. European Respiratory Review [internet]. 2016 [cited 2022 August 22]. Available from: https://err.ersjournals.com/content/25/140/189#sec-10
  13. Skok K, Hladnik G, Grm A, Crnjac A. Malignant Pleural Effusion and its Current Management: A Review. Medicina [internet]. 2019 August 15 [cited 2022 August 22]. Available from: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6723530/
  14. RadiologyInfo.org. Thoracentesis [internet]. 2020 June 15 [cited 2022 August 22]. Available from: https://www.radiologyinfo.org/en/info/thoracentesis#:~:text=limitations%20of%20Thoracentesis%3F-,What%20is%20a%20Thoracentesis%3F,inside%20of%20the%20chest%20wall
  15. RadiologyInfo.org. Chest Tube Placement (Thoracostomy) and Pleurodesis [internet]. 2020 August 24 [cited 2022 August 22]. Available from: https://www.radiologyinfo.org/en/info/thoracostomy
  16. SickKids. Catheter Drainage for Pleural Effusion (PleurX drainage system) [internet]. 2019 July 25 [cited 2022 August 22]. Available from: https://www.aboutkidshealth.ca/pleuraleffusion#:~:text=For%20a%20pleural%20effusion%2C%20a,improve%20their%20quality%20of%20life
This content is purely informational and isn’t medical guidance. It shouldn’t replace professional medical counsel. Always consult your physician regarding treatment risks and benefits. See our editorial standards for more details.

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Brianna Jacobs

Bachelor of Science - BS, Biomedical Sciences, General, University of Birmingham, England
Brianna is a Second Year Biomedical Science Student who experienced Medical Writing Intern.

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