Once the malignant mesothelioma has been found, more cancer tests will be done to find out if cancer cells have spread around to other parts of the body. This process is called mesothelioma staging. The doctor needs to know the stage of the cancer to plan the treatments.

The staging of mesothelioma is based on imaging studies such as x-rays, CT scans, and MRI scans. The cancer treatment and outlook for patients with mesothelioma depends largely on the stage (extent of spread) of their cancer. Since pleural mesothelioma happens most frequently and has been the most studied, it is the only mesothelioma where a staging classification system exists. The following cancer stages are used for malignant mesothelioma:

Butchart Staging System

The Butchart staging system most often used for mesothelioma. The Butchart system is based mostly on the extent of the primary cancer tumor mass, and divides all mesotheliomas into stages I through IV.

Stage I: The mesothelioma is present within the right or left pleura, and may also involve the lung, pericardium, or diaphragm (the muscle that separates the chest from the abdomen) on the same side of the body.

Stage II: Mesothelioma has invaded the chest wall or involves the esophagus (the food passage connecting the throat to the stomach), heart, or pleura on both sides. The lymph nodes in the patient's chest may also be involved.

Stage III: Mesothelioma has now penetrated through the diaphragm into the peritoneum (lining of the abdominal cavity). Some lymph nodes beyond those in the chest may also be involved at this point.

Stage IV: There is strong evidence of distant metastases (which is the spreading of cancerous cells via the bloodstream to other organs).


TNM Cancer Staging System

Yet another staging system has recently been created by the American Joint Committee on Cancer (AJCC). Called a TNM system, similar to staging systems that are used for most other cancers. The 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 a TNM staging, information about the lung 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. There are some minor differences that exist between the AJCC TNM staging system and the Butchart staging system.

Stage I: The mesothelioma involves the right or left pleura. The cancer may also have spread into the lung, pericardium, or diaphragm on the same side, but it has not yet spread to the lymph nodes.

Stage II: Here the mesothelioma has spread from the pleura on one side to the nearby peribronchial and/or hilar lymph nodes next to the lung on the same side. And it may have also spread into the lung, pericardium, or diaphragm on the same side.

Stage III: Mesothelioma spreads into the chest wall muscle, ribs, heart, esophagus, or other organs in the chest on the same side as the primary tumor, with or without spreading to subcarinal and/or mediastinal lymph nodes on the same side as the main tumor. The subcarinal nodes are located at the point where the windpipe branches to the left and right lungs. Mediastinal lymph nodes are located in the area behind the chest bone in front of the heart. Mesotheliomas with the same extent of local spread as in Stage II that have also spread to subcarinal and/or mediastinal lymph nodes on the same side are also included in Stage III.

Stage IV: Mesothelioma spreading into the lymph nodes in the chest on the side opposite that of the primary lung tumor, or directly extends to the pleura or lung on the opposite side, or directly extends into the peritoneum, or directly extends into organs in the abdominal cavity or neck. Any mesothelioma with evidence of distant metastases (spreading to other organs via the bloodstream) or spread to organs beyond the chest or abdomen is included in this stage.

Although the TNM classification is the most detailed and precise, the old original Butchart staging system is still used most often to describe the spread of pleural mesothelioma. To be able to understand these staging systems for mesothelioma is important both for estimating and better understanding prognosis, and also for assessing the therapeutic options.