Detailed staging of mesothelioma
Staging systems are constantly being updated to help doctor plan the best treatment and help give an idea of the likely outcome.
Many staging systems are based on the TNM system:
T describes the size of the tumour.
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.
Different staging systems have been used for mesothelioma. The staging system that’s most commonly used is known as the International Mesothelioma Interest Group (IMIG) system. It’s also based on the TNM system.
A simplified version of the IMIG system is described below. You may find it helpful to refer to the diagram showing the structure of the lungs and pleura in the section explaining what mesothelioma is.
Cancer cells are found in the pleura around the lung on one side of the chest.
Stage 1a Cancer cells are only found in the outer layer of the pleura (parietal pleura).
Stage 1b Cancer cells are also found in the inner layer of the pleura (visceral pleura).
The cancer has spread to both layers of the pleura and has either spread into the muscle of the diaphragm or into the lung tissue on one side of the chest.
The cancer has spread deeper into the tissues around the pleura. It may have spread to:
the chest wall
the fatty tissue in the centre of the chest
the tissue that separates the ribs from the pleura
the outer lining of the heart (pericardium).
Or, it may have spread to local lymph nodes.
The cancer has spread deeply into the tissues close to the
pleura. It may have spread to:
the pleura on the other side of the chest
the diaphragm and beyond it to the lining surrounding the abdomen (peritoneum)
the internal surface of the heart pericardium and into the muscle of the heart.
Or, it may have spread to the lymph nodes on the other side of the chest or the lymph nodes above the collar bone on the same or other side of the chest.
Or, it may have spread to distant organs or tissues.
There isn’t a specific staging system for peritoneal mesothelioma but doctors sometimes use the TNM staging system outlined above.