A pleural effusion is a buildup of extra fluid in the pleural space, which is the space between the edge of the lungs and the chest wall. About half of people with cancer develop a pleural effusion. More than 75% of people with a malignant pleural effusion have lymphoma or cancers of the breast, lung, or ovary. Although a malignant pleural effusion is treatable, it can be a serious, potentially life-threatening condition.
Cancer growing in the pleural space causes a malignant pleural effusion. This condition is considered a sign of metastatic cancer, or cancer that has spread to other areas of the body. Therefore, most people with a pleural effusion are referred to hospice care .
Relieving side effects, also called symptom management, palliative care , or supportive care, is an important part of cancer care and treatment. Talk with your health care team about any symptoms you experience, including any symptoms of malignant pleural effusion or a change in symptoms.
People with a pleural effusion may experience the following symptoms:
- Dyspnea (shortness of breath )
- Dry cough
- Pain 
- Feeling of chest heaviness
- Inability to exercise
- Malaise (feeling unwell)
The following tests may help diagnose a malignant pleural effusion, find the exact location of the pleural effusion, or plan treatment:
- A physical examination
- A chest x-ray (a picture of the inside of the body), which shows the buildup of fluid
- Computed tomography (CT or CAT)  (an imaging test that creates a three-dimensional picture of the inside of the body with an x-ray machine).
- Ultrasound  (an imaging test that uses sound waves to create a picture of the inside of the body).
- Thoracentesis (the removal and analysis of fluid from the pleural cavity with a needle)
A pleural effusion often requires treatment in a hospital or clinic. The most common treatment is to drain the malignant pleural fluid. This may be done in several ways:
- Thoracentesis (see above)
- Tube thoracostomy (insertion of a tube in the chest) for about 24 hours, followed by pleurodesis (a process in which substances, such as talc, are used to try to get the edge of the lung to stick to the chest wall to decrease the chance of the fluid returning)
- The insertion of a catheter  (a small tube placed temporarily into the pleural space) that allows you or your family member to drain the fluid into a bottle as needed or directed, or shunt (a device used to bypass or divert fluid from one place to another) to drain excess fluid.