Mesothelioma stages

Staging for mesothelioma refers to the size of the cancer and whether it has spread. There are different staging systems: TNM, IMIG and PCI.

What are the stages for mesothelioma?

The stage of a cancer refers to its size and if it has spread beyond the area of the body where it first started. Knowing the stage of the cancer helps your doctors decide on the best treatment for you.

There are a number of different staging systems. Many are based on the TNM system:

  • T describes the size of the cancer.
  • N describes whether the cancer has spread to the lymph nodes and which nodes are involved. For example, N0 means that no lymph nodes are affected, while N1 means there are cancer cells in the lymph nodes.
  • M describes whether the cancer has spread (metastasised) to another part of the body. For example, M0 means the cancer has not spread to other parts of the body, while M1 means the cancer has spread to other parts of the body.

There are different staging systems for the different mesothelioma types.

We understand that waiting to know the stage and grade of your cancer can be a worrying time. We're here if you need someone to talk to. You can:

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Staging for pleural mesothelioma

The staging system that is often used for pleural mesothelioma is called the International Mesothelioma Interest Group (IMIG) system. It is based on the TNM system, but has been adapted for mesothelioma.

This is a simplified version of the IMIG system.

Stage 1

Cancer cells are only in the inner or outer pleura, in one side of the chest. The cancer has not spread to the lymph nodes or outside of the chest.

Stage 1 is divided into the following:

  • Stage 1a – Cancer cells are only in one or more areas in the inner or outer layer of the pleura.
  • Stage 1b – Cancer cells have broken through the pleura into the tissue just beneath, for example to the surface of the lung or the diaphragm.

Stage 2

The cancer is in the same areas as stage 1 but has also spread to nearby lymph nodes (N1).

Stage 3

Stage 3 is divided into the following:

  • Stage 3a – Cancer cells have spread deeper into the tissues beneath the pleura. For example, they have spread:
    • deeper into the tissues in the chest wall
    • into, but not through, the outer lining of the heart (pericardium) to fatty tissue in the centre of the chest, and nearby nodes (N1).
  • Stage 3b – Or, cancer cells have spread further into the chest wall, through the pericardium or to nearby organs. It may or may not have spread to lymph nodes in the centre of the chest, or lymph nodes further away from the lungs (N2).

Stage 4

The cancer has spread outside of the chest to another area of the body (metastasis or M1).


Structure of the lungs and pleura
Image: Structure of the lungs and pleura

Staging for peritoneal mesothelioma

There is no specific staging system for peritoneal mesothelioma. But doctors sometimes use an adapted TNM system called the Peritoneal Cancer Index (PCI).

This looks at:

  • the number of tumours in the peritoneum
  • the size of the tumours
  • where the tumours are in the tummy area (abdomen).
  • whether the cancer has spread outside the peritoneum or to any lymph nodes.

PCI is only used at specialist centres. You can ask your doctors for more information if you have any questions.

About our information

  • References

    Below is a sample of the sources used in our mesothelioma information. If you would like more information about the sources we use, please contact us at

    Woolhouse I et al. British Thoracic Society Guideline for the investigation and management of malignant pleural mesothelioma. Thorax. 2018.

    Thomas A et al. Mesothelioma. BMJ Best Practice. 2019.

    Baas P et al. Malignant pleural mesothelioma: ESMO Clinical Practice Guidelines for diagnosis, treatment and follow-up.  Annals of Oncology. 26 (Supplement 5): v31–v39. 2015. Available from:

    Kusamara S et al. Peritoneal mesothelioma: PSOGI/EURACAN clinical practice guidelines for diagnosis, treatment and follow-up. European Journal of Surgical Oncology. March 2020.

  • Reviewers

    This information has been written, revised and edited by Macmillan Cancer Support’s Cancer Information Development team. It has been reviewed by expert medical and health professionals and people living with cancer. It has been approved by Senior Medical Editor, Dr David Gilligan, Consultant Clinical Oncologist.

    Our cancer information has been awarded the PIF TICK. Created by the Patient Information Forum, this quality mark shows we meet PIF’s 10 criteria for trustworthy health information.

Date reviewed

Reviewed: 01 August 2021
Next review: 01 August 2024
Trusted Information Creator - Patient Information Forum
Trusted Information Creator - Patient Information Forum

Our cancer information meets the PIF TICK quality mark.

This means it is easy to use, up-to-date and based on the latest evidence. Learn more about how we produce our information.