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

Staging for mesothelioma

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

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

  • 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 types of mesothelioma.

Staging for pleural mesothelioma

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

A simplified version of the IMIG system is described below.

Stage 1

Cancer cells are only found 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:

  • Stage 1a – Cancer cells are only found 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.

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:

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

Stage 4

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

The illustration shows the lungs in the chest. It shows the windpipe (trachea) coming down from the neck into the chest. About halfway down the chest, the windpipe divides into two tubes. One tube goes into the left lung. The other tube goes into the right lung. There are ribs around the outer side of each lung. Underneath the lungs, and going across the width of the body, is a muscle called the diaphragm.   Surrounding each lung is a thin lining (membrane), which has two layers. This is called the pleura. The layer closest to each lung is called the inner pleura. The layer which lines the chest wall is called the outer pleura. There is a small space between the two layers of the pleura. This space is called the pleural cavity.  There are groups of pea-sized lymph nodes in the chest. They are connected to each other by fine tubes. The lymph nodes are close to the windpipe. There are also lymph nodes on each side of the neck and in the shoulder area.

Staging for peritoneal mesothelioma

There is no specific staging system for peritoneal mesothelioma. But doctors sometimes use the TNM system.

Some doctors 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).

This is put together with information about whether the cancer has spread to any lymph nodes or to any areas outside of the peritoneum. PCI is not routinely used in the UK. But you can ask your doctors for more information if you have any questions.

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