Staging is the process of finding out how far the cancer has spread. Staging of mesothelioma is based on imaging studies such as x-rays, CT scans, and MRI scans. The treatment and outlook for patients with mesothelioma largely depends on the stage (extent of spread) of their cancer. Since pleural mesothelioma occurs most frequently and has been studied the most, it is the only mesothelioma for which a staging classification exists.

The major staging system has recently been developed by the International Mesothelioma Interest Group and adopted by the American Joint Committee on Cancer (AJCC). This is a TNM system, similar to staging systems used for most other cancers. 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 (spread to distant organs). In TNM staging, information about the tumor, lymph nodes, and metastasis is combined in a process called stage grouping to assign a stage described by Roman numerals from I to IV.

T Stages

T1: Mesothelioma involves either the right or left pleura lining the chest. It has only spread to the pleura covering the lung, with the exception of possibly a few other small spots.

T2: Mesothelioma involves either the right or left pleura lining the chest and has spread from the lining of the chest into 1) the outer lining of the lung, 2) the diaphragm, or 3) into the lung itself.

T3: Mesothelioma involves either the right or left pleura lining the chest and has spread into 1) the first layer of the chest wall, 2) the fatty part of the mediastinum, 3) a single place in the chest wall, or 4) the outer covering layer of the heart.

T4: Mesothelioma involves either the right or left pleura lining the chest and has spread 1) into the chest wall, either muscle or ribs, 2) through the diaphragm, 3) into any organ contained in the mediastinum (esophagus, trachea, thymus, blood vessels), 4) into the spine, 5) across to the pleura on the other side of the chest, 6) through the heart lining or into the heart itself, or 7) into the brachial plexus (nerves leading to the arm).

N Stages

N0: No spread to lymph nodes.

N1: Spread to lymph nodes on the same side of the chest as the mesothelioma.

N2: Spread to lymph nodes around the point where the windpipe branches into the left and right bronchi or to lymph nodes in the space behind the chest bone and in front of the heart (mediastinum). Affected lymph nodes are on the same side of the cancerous lung.

N3: Spread to lymph nodes near the collarbone on either side, to hilar or mediastinal lymph nodes on the side opposite the cancerous lung.

M Stages

M0: No spread to distant organs or areas.

M1: The cancer has spread distantly.

Stage Grouping for Pleural Mesothelioma

Once the T, N, and M categories have been assigned, this information is combined (stage grouping) to assign an overall stage of I, II, III, or IV. Patients with lower stage numbers have a better prognosis.

Stage I (T1, N0, M0): Mesothelioma involves either the right or left pleura lining the chest. It has only spread to the outer lining of the lung in, at most, a few small spots. It has not spread to the lymph nodes or distant sites.

Stage II (T2, N0, M0): Mesothelioma involves either the right or left pleura lining the chest and has spread from the lining of the chest into 1) the outer lining of the lung, 2) the diaphragm, or 3) into the lung itself. It has not spread to the lymph nodes or distant sites.

Stage III (T1 or 2, N1 or 2, M0; OR T3, N0-2, M0): Mesothelioma involves either the right or left pleura lining the chest and may or may not have spread from the lining of the chest into 1) the outer lining of the lung, 2) the diaphragm, 3) into the lung itself and has spread to lymph nodes anywhere in the chest on the same side as the tumor, but has not spread to distant sites; OR Mesothelioma involves either the right or left pleura lining the chest and has spread into 1) the first layer of the chest wall, or 2) the fatty part of the mediastinum, or 3) a single place in the chest wall or 4) the outer covering layer of the heart and may or may not have spread to lymph nodes but not as far as to lymph nodes near the collarbone or on the opposite side of the chest. It has not spread to distant sites.

Stage IV (T4, any N, M0; OR any T, N3, M0; OR any T, any N, M1): Mesothelioma involves either the right or left pleura lining the chest and has spread 1) into the chest wall, either muscle or ribs, 2) through the diaphragm, 3) into any organ contained in the mediastinum (esophagus, trachea, thymus, blood vessels), 4) into the spine, 5) across to the pleura on the other side of the chest, 6) through the heart lining or into the heart itself, or 7) into the brachial plexus (nerves leading to the arm), and may or may not have spread to lymph nodes anywhere, but has not spread to distant sites; OR the tumor is of any size, but has spread to lymph nodes near the collarbone on either side, to hilar or mediastinal lymph nodes on the side opposite the cancerous lung but not to distant sites; OR the mesothelioma has spread to distant sites.