Staging is the process of finding out how far the mesothelioma cancer has spread. Doctors determine which treatments to use based on the mesothelioma stage, or the severity of the disease. The major mesothelioma staging system used is a TNM system, similar to the system used for most other cancers. The mesothelioma stages are as follows: T stands for tumor (its size and how far it has spread to nearby organs), N stands for spread to lymph nodes, and M is for metastasis (whether it has spread to distant organs).

Mesothelioma stage grouping assigns a number to represent information about tumor, lymph nodes, and metastasis.

T Mesothelioma Stages

• T1: The cancer has only spread to the outer lining of either the right or the left lung.
• T2: The cancer has spread to the outer lining of the lung, to the diaphragm, and or into the lung itself on either the right or the left side.
• T3: The cancer has spread into the first layer of the chest wall, the fatty part of the mediastinum (heart, esophagus, trachea, and lymph nodes in the chest), a single place in the chest wall, or the outer covering of the heart.
• T4: The cancer has spread into the chest wall-either muscle or ribs, through the diaphragm, into any organ of the mediastinum, into the spine, into both sides of the chest, through the heart lining or into the heart, or into the nerves leading into the arm.

N Mesothelioma Stages

• N0: No spread to lymph nodes.
• N1: Spread to lymph nodes only on the same side of the chest as the mesothelioma.
• N2: Spread to lymph nodes where the windpipe branches into the bronchi, or to lymph nodes in the mediastinum on the same side of the chest as the mesothelioma.
• N3: Spread to lymph nodes on either side of the collarbone or to lymph nodes on the opposite side of the chest from the mesothelioma.

M Mesothelioma Stages

• M0: No spread to distant organs or areas.
• M1: The cancer has spread distantly.

After all TNM categories and numbers have been assigned, doctors can assign an overall mesothelioma stage of I, II, III, or IV. Patients with lower stage numbers have a better prognosis, or life expectancy.