Treatment options are often determined by the stage of mesothelioma. There are three staging systems used for pleural mesothelioma and each measures different variables; peritoneal mesothelioma is not staged.

The oldest and most often used staging system is the Butchart System, which is based primarily on the extent of primary tumor mass. The more recent developed TNM system is based on variables of tumor mass and spread, lymph node involvement, and metastasis. The Brigham System is the latest staging system, which stages mesothelioma according to resectability (the ability to surgically remove) and lymph node involvement.

Butchart System - extent of primary tumor mass

• Stage I: Mesothelioma is present in the right or left pleura and may also involve the diaphragm on the same side.
• Stage II: Mesothelioma invades the chest wall or involves the esophagus, heart, or pleura on both sides. Lymph nodes in the chest may also be involved.
• Stage III: Mesothelioma has penetrated through the diaphragm into the lining of the abdominal cavity or peritoneum. Lymph nodes beyond those in the chest may also be involved.
• Stage IV: There is evidence of metastasis or spread through the bloodstream to other organs.

TNM System - variables of T (tumor), N (lymph nodes), M (metastasis)

• Stage I: Mesothelioma involves right or left pleura and may also have spread to the lung, pericardium, or diaphragm on the same side. Lymph nodes are not involved.
• Stage II: Mesothelioma has spread from the pleura on one side to nearby lymph nodes next to the lung on the same side. It may also have spread into the lung, pericardium, or diaphragm on the same side.
• Stage III: Mesothelioma is now in the chest wall, muscle, ribs, heart, esophagus, or other organs in the chest on the same side with or without spread to lymph nodes on the same side as the primary tumor.
• Stage IV: Mesothelioma has spread into the lymph nodes in the chest on the side opposite the primary tumor, or extends to the pleura or lung on the opposite side, or directly extends into organs in the abdominal cavity or neck. Any distant metastases is included in this stage.

Brigham System - variables of tumor resectability and nodal status

• Stage I: Resectable mesothelioma and no lymph node involvement
• Stage II: Resectable mesothelioma but with lymph node involvement
• Stage III: Unresectable mesothelioma extending into chest wall, heart, or through diaphragm, peritoneum; with or without extrathoracic lymph node involvement
• Stage IV: Distant metastatic disease