What causes malignant pleural effusion?

Lung cancer, breast cancer, lymphoma, leukaemia and mesothelioma can cause it. Other cancers may also spread to the pleura.

The pleura are thin layers of tissue covering the lungs and lining the inside of the chest. A small amount of fluid normally lets these layers glide during breathing. Cancer cells can irritate the pleura, increase fluid production or obstruct lymph channels that usually remove fluid. The resulting collection may press on a lung and cause breathlessness, cough, chest pressure or pain with a deep breath.

A pleural effusion in someone with cancer is not automatically malignant. Infection, a blood clot in the lung, heart problems, poor nutrition, a partly collapsed lung and some cancer treatments can also cause fluid around a lung.

Report new or worsening breathlessness, cough or chest discomfort promptly to your cancer or respiratory team. Imaging can show where the fluid is and how much is present. A clinician may remove a sample with a needle and examine it for cancer cells, infection and other clues; occasionally, a pleural biopsy is needed when the cause remains uncertain.

Care is tailored to symptoms, whether the fluid returns, whether the lung expands after drainage and the plan for the underlying cancer. Options may include draining the fluid, placing a longer-term pleural catheter, sealing the pleural space, treating the cancer, and supportive care for breathlessness.

Contact your care team urgently if breathing becomes noticeably harder, you cannot manage usual activities, chest pain is new, or fever develops. Call local emergency services for severe or sudden breathlessness, blue or grey lips, fainting, confusion, or chest pain accompanied by sweating or marked weakness. These signs need rapid assessment regardless of their cause.

Ask whether the fluid has been confirmed as malignant, what the imaging and fluid analysis showed, whether another condition could be contributing, and how likely the collection is to return. It can also help to discuss which drainage approach fits your breathing symptoms and daily routine, what warning signs to watch for after a procedure, and whom to contact outside clinic hours.