# Malignant pleural effusion

Source: https://onco.cc/terms/malignant-pleural-effusion/  
OnCo record `malignant-pleural-effusion` (Term). Data CC BY-NC 4.0, attribute "Data from OnCo (onco.cc)"; commercial use needs a licence.

## TL;DR

Fluid collecting in the space between the lung and the chest wall because cancer has reached the lining. It makes people breathless, it comes back after it is drained, and the decision is not whether to drain it but how to stop it returning.

## Summary

Cancer on the pleural surface leaks fluid into the pleural space faster than the lymphatics can clear it; lung cancer, breast cancer and mesothelioma are the commonest causes. Fluid in that space is also an M1a descriptor in the TNM classification, so its presence usually places a lung cancer at stage IV whatever the size of the primary. Symptomatically it causes breathlessness, a dry cough and sometimes chest discomfort, and the fluid can be removed in minutes at the bedside with lasting relief. The problem is recurrence. NICE NG122 asks teams to perform pleural aspiration or drainage to relieve symptoms, and to offer talc pleurodesis to people who would get long-term benefit from repeated drainage: talc is instilled to stick the two pleural layers together so that no space is left for fluid to collect. An indwelling pleural catheter, drained at home, is the alternative where the lung will not re-expand or where a person prefers to avoid admission. The choice turns on how trapped the lung is, how long the person is expected to live and how much time in hospital the treatment costs them.

## Fields

- Kind: Term
- Last checked: 2026-09-25
- Also known as: pleural effusion in cancer; malignant effusion; fluid on the lung; malignant pleural fluid; recurrent pleural effusion
- Tags: lung

## Sources

- Wikipedia: https://en.wikipedia.org/wiki/Pleural_effusion
- NICE NG122: lung cancer, palliative interventions and supportive and palliative care (1.13 to 1.18): https://www.nice.org.uk/guidance/ng122/chapter/Palliative-interventions-and-supportive-and-palliative-care
- Br J Radiol 2025: something old something new, introduction to the ninth edition TNM classification of lung cancer (effective 1 January 2025): https://doi.org/10.1093/bjr/tqaf161

## Connected records

- cancers: [Lung cancer (all types)](https://onco.cc/cancers/lung-cancer/), [Mesothelioma](https://onco.cc/cancers/mesothelioma/), [Non-small-cell lung cancer](https://onco.cc/cancers/nsclc/), [Pleural mesothelioma](https://onco.cc/cancers/pleural-mesothelioma/), [Small-cell lung cancer](https://onco.cc/cancers/sclc/)
- terms: [Malignant pleural effusion and ascites](https://onco.cc/terms/pleural-effusion/), [Performance status (ECOG, Karnofsky)](https://onco.cc/terms/performance-status/), [Pleura](https://onco.cc/terms/pleura/), [Pleurodesis and indwelling pleural catheter](https://onco.cc/terms/pleurodesis/), [TNM 9: what changed in lung cancer staging](https://onco.cc/terms/tnm-9-lung-cancer/)

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