What are the staging systems of Mesothelioma?

Mesothelioma is a cancer of the mesothelium, or lining, of the chest, lungs, or abdomen. Mesothelioma that affects the pleural or chest cavity is called pleural mesothelioma and is the most common form. Peritoneal mesothelioma affects the peritoneum, which is the tissue that lines the organs in the abdomen. Since nearly all cases of malignant mesothelioma are caused by asbestos exposure, mesothelioma is sometimes called asbestos cancer.

Because mesothelioma can take up to five decades to develop after the asbestos exposure that caused it, and because the disease is relatively obscure, diagnosis often does not occur until the later stages. Compounding these difficulties is the fact that mesothelioma symptoms often mimic other diseases. Correct diagnosis and staging is both difficult and imperative.

Staging is used to describe severity of a patient's mesothelioma based on the condition of the primary tumor and how far it has spread in the body. Staging is important because it helps the doctor choose an appropriate treatment, it is used to estimate the patient's prognosis, and it helps identify clinical trials that may be appropriate for the patient.

The determination of staging can be clinical or pathological. Clinical staging relies on scanning tests and x-rays. Pathological staging refers to staging done at surgery.

For pleural mesothelioma there are three systems of classification used: the Butchart System, which is the oldest system for staging mesothelioma; the Brigham System, which focuses on the ability to surgically remove the mesothelioma, and the TNM Staging system, which is increasingly used by major cancer centers as a way of more precisely identifying the stage of cancers.

At present, there is no established staging system for peritoneal mesothelioma; if the disease is staged, the TNM system is generally used.

The TNM System

The TNM system breaks down as follows:

• T = Primary tumor
• N = Regional lymph nodes
• M = Distant metastasis (the spread of cancer through the bloodstream to other organs)

A number is used with each letter to show the size of the tumor and how much it has spread. For "T" and "N", "0" is used to indicate no invasion of tissues or spread; "4" means extensive involvement. For "M", "0" means no metastasis and "1" means there are metastases. For example, a cancer that is classified as T2N0M0 is one that has a measurable, mid-sized tumor but has not spread to lymph nodes and shows no metastases.

When applied to pleural mesothelioma, TNM information is used to categorize the disease into four stages:

Stage I: The mesothelioma involves the lining on either the left or right side of the chest. The cancer can be found only to the outer lining of the lung, is present in only a few small spots and has not yet reached the lymph nodes.

Stage II: The mesothelioma involves the lining on either the left or right side of the chest and has spread into the outer lining of the lung, the diaphragm (the muscle separating the chest from the abdomen), or into the lung itself.

Stage III: The mesothelioma involves the lining on either the left or right side of the chest and has spread into the first layer of the chest wall, the fatty part of the mediastinum (the space in the chest cavity behind the breastbone and in between the two pleural sacs that contain the lungs), a single place in the chest wall, the pericardium, or lymph nodes anywhere in the same side of the chest.

Stage IV: The mesothelioma involves the lining on either the left or right side of the chest and has spread into the chest wall; through the diaphragm; into the esophagus, trachea, thymus, or blood vessels contained in the mediastinum; into the spine; across to the lining on the other side of the chest; through the pericardium or into the heart itself; into the nerves leading to the arm; into lymph nodes outside that side of the chest; or to other organs via the bloodstream.

For peritoneal mesothelioma, the TNM stages are:

Stage I: The mesothelioma is localized, with the tumor able to be completely removed surgically.

Stage II: The mesothelioma is contained within the abdominal cavity on peritoneal and organ surfaces and surgical removal of much of the tumor, but not all of it, is possible.

Stage III: The mesothelioma is contained within the abdominal cavity but has spread to organs such as the colon or liver.

Stage IV: The mesothelioma is no longer contained within the abdominal cavity but has spread to other areas of the body.

The Brigham System

The four stages of pleural mesothelioma under the Brigham system are as follows:

Stage I: The tumor can be removed surgically and no lymph nodes are involved.

Stage II: The tumor can be removed surgically, but cancer is present in the lymph nodes.

Stage III: The tumor cannot be removed surgically because it extends into the chest wall, to the heart, or through the diaphragm into the peritoneum. Lymph nodes outside the chest may or may not have cancerous cells.

Stage IV: The cancer has spread to other parts of the body.

The Butchart System

Stages one through four of the Butchart system are as follows:

Stage I: The mesothelioma can be found within the pleura on one side of the chest. It may also involve the lung, pericardium, or diaphragm on the same side.

Stage II: The mesothelioma invades the chest wall or involves the esophagus, heart, or pleura on both sides. The lymph nodes in the chest may also be involved.
 
Stage III: Mesothelioma has penetrated through the diaphragm into the peritoneum. Lymph nodes beyond those in the chest may also be involved.
 
Stage IV: There is evidence of distant metastases.

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