TNM Staging System

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TNM Staging System

Also called the IMIG Staging System, this is the most widely used system for pleural mesothelioma. Doctors sometimes use it for other types of mesothelioma as well.

The abbreviation TNM signifies three different parts of a diagnosis. Doctors add a number after each letter to describe how far cancer has advanced. As tumor size increases and cancer invades more structures, the number increases.

T describes tumor size and location, ranging from T0 to T4.

N describes whether lymph nodes are affected, ranging from N0 to N3.

M describes whether the tumors have metastasized (spread through the bloodstream to other parts of the body), ranging from M0 to M1.

Doctors use the TNM framework to stage many different types of cancer. In 1995, the International Mesothelioma Interest Group (IMIG) modified this system specifically for asbestos-related cancers because of the lack of a universally accepted staging system.

After evaluating a case, doctors assign a value to each part of the TNM system. Next, they use this information to give cancer a stage. For example, TNM staging guidelines say a T1N1M0 mesothelioma is a stage 3 cancer.

Stage 1
T1, N0, M0: Mesothelioma has developed in the pleura lining one side of the chest wall and may affect the lining near the breathing muscle (diaphragm) or the area between the lungs (mediastinum).

Stage 2
T2, N0, M0: Mesothelioma has grown in the pleura lining one side of the chest wall and the lining near the diaphragm, the mediastinum, and the lung, and it has also grown into the diaphragm or the lung itself.

Stage 3
T3, N0–N2, M0: Mesothelioma has spread from the pleura into part of the chest wall, the outer layer of the heart sac or the fatty tissue in the mediastinum.


T1–T2, N1–N2, M0: The primary tumor mass has not spread far beyond the pleura, but mesothelioma cells have spread to lymph nodes near the tumor.

Stage 4
T4: Mesothelioma has penetrated into the abdominal lining, the spine, the deep layers of the chest wall, the pleura on the other side of the chest, or any vital organ between the lungs.


N3: Mesothelioma cells have spread to lymph nodes far from the primary tumor mass.


M1: Mesothelioma tumors have developed in distant parts of the body.

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