Stages of Mesothelioma Cancer

Mesothelioma, or more precisely malignant mesothelioma, is a form of cancer that forms in the mesothelium, which is a tissue layer in vital organs such as the lungs, abdomen, and heart. Mesothelioma is most commonly caused by asbestos exposure. Fortunately it is a rare from of cancer.

Defining the stages of mesothelioma helps determine the extent of cancer in a patient's body. Catching it in the early stages is extremely important in extending the patient's life. Stages identify clinical trials that can benefit a patient. It also helps to estimate the prognosis and to plan treatment options.

There are three main staging systems for mesothelioma. They are the Butchart System, Brigham, and the TNM system. The most commonly used is the TNM Classification of Malignant Tumors ("TNM"). In the acronym, the T stands for tumor, which describes the size of the tumor whether it has entered into nearby tissue. The N is for the lymph nodes, and the M is for metastasis, whether the cancer has spread to other parts of the body. Staging is mostly commonly done in pleural mesothelioma, which is in the lining of the lungs.

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 staging system used in the past for mesothelioma is the Butchart System. This system is based mainly on the extent of the primary tumor mass, and divides mesotheliomas into stages I through IV. Many doctors will still use this system.

Stage I
Mesothelioma is present on one side of the chest only and isn’t growing into the chest wall.

Stage II
Mesothelioma invades the chest wall or involves the esophagus (food passage connecting the throat to the stomach), heart, or has grown into the pleura on the other side of the chest.. The lymph nodes in the chest may also be involved.

Stage III
Mesothelioma has grown through the diaphragm into the peritoneum (lining of the abdominal cavity) or has spread to lymph nodes beyond those in the chest.

Stage IV
Mesothelioma has spread through the bloodstream to other organs (metastases).

Another 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. Major cancer centers are beginning to use this system instead of the Butchart staging because it more accurately depicts the extent of tumor.

Stage I
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 yet spread to the lymph nodes.

Stage II
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 or 2) the diaphragm or 3) into the lung itself.

Stage III
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 or 5) lymph nodes anywhere in the same side of the chest.

Stage IV
Mesothelioma involves either the right or left pleura lining the chest and has spread 1) into the chest wall, either muscle or ribs, or 2) through the diaphragm, or 3) into any organ contained in the mediastinum (esophagus, trachea, thymus, blood vessels), or 4) into the spine, or 5) across to the pleura on the other side of the chest, or 6) through the heart lining or into the heart itself, or 7) into the brachial plexus (nerves leading to the arm), or 8) into lymph nodes outside that side of the chest, or 9) spread to other organs through the bloodstream.

Experts recommend that this staging system should be used instead of the original Butchart staging system.