Stages of mesothelioma

The stage of a cancer tells the doctor where it is, how big it is and whether it has spread. The tests and scans you have when diagnosing your cancer give some information about the stage. Knowing the stage helps your doctor decide about the treatment you need.

Most people who are diagnosed with mesothelioma have an advanced stage of cancer.

IMIG stages

The staging system most commonly used in the UK for pleural mesothelioma is called the International Mesothelioma Interest Group (IMIG) system. 

It is based on the TNM (tumour, node, metastasis) system, which is used for many different cancers. This describes:

  • the size and position of the primary mesothelioma tumour (T)
  • whether mesothelioma cells have spread to nearby lymph nodes (N)
  • whether mesothelioma cells have spread to other parts of the body - metastases (M)

Once the TNM categories have been decided, this information is grouped together to give the number stage. The number system divides mesothelioma in 4 stages, from 1 to 4. Stage 1 is the earliest stage and stage 4 is the most advanced stage.

Stage 1

Mesothelioma cells are in the pleura around the lung on one side of your chest.

Stage 1a 

Mesothelioma cells are in the outer layer of the pleura (parietal pleura) on one side of the chest.

Stage 1b

Mesothelioma cells are in the inner layer of the pleura (visceral pleura), but only on one side of the chest. They have not spread to your lung tissue or diaphragm.

Stage 2

Mesothelioma has spread to both layers of the pleura on one side of the body, and at least one of the following:

  • has started to spread into the diaphragm muscle
  • has started to spread to the lung tissue

Stage 3

Mesothelioma has started to spread to the chest wall or the covering of the heart (pericardium) but is still potentially removable by surgery. Or it has spread to the lymph nodes on the same side of the chest.

Stage 4

Stage 4 means that mesothelioma cannot be removed by surgery. This is because it has spread to different parts of the chest wall or has grown through:

  • the diaphragm into the lining of the abdomen (peritoneum)
  • the pleura on the other side of the body
  • the chest organs
  • the inner layer of the pericardium

Or it has spread to the lymph nodes on the other side of the chest, or above the collarbone. Or has spread to other parts of the body.

Peritoneal mesothelioma stages

There is no established staging system for peritoneal mesothelioma. Sometimes the doctors may use the TNM system used for pleural mesothelioma.


The stage of your cancer helps your doctor to decide which treatment you need. Treatment also depends on:

  • your type of mesothelioma (the type of cells the cancer started in)
  • how the cancer is likely to behave (the grade)
  • other health conditions that you have
Last reviewed: 
21 May 2021
Next review due: 
21 May 2024
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    American Joint Committee on Cancer
    Springer, 2010

  • Biology and management of malignant pleural mesothelioma. 

    P Zucali and others

    European Journal of Cancer, (2006). 42(16), 2706-2714

  • Malignant pleural mesothelioma: ESMO Clinical Practice Guidelines for diagnosis, treatment and follow-up
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    Ann als of Oncology (2015) 26 (suppl 5): v31-v39

  • Cancer: Principles and Practice of Oncology (11th edition)
    VT De Vita, TS Lawrence and SA Rosenberg
    Lippincott, Williams and Wilkins, 2018

  • Peritoneal mesothelioma: PSOGI/EURACAN clinical practice guidelines for diagnosis, treatment and follow-up 
    S. Kusamura and others 
    European Journal of Surgical Oncology, 2020. Vol 47. Pages 36-59 

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