Stages of mesothelioma is based on the recommendation by the International Mesothelioma Interest Group. TNM classification of the primary tumor, lymph node involvement, and distant metastasis is performed. Mesothelioma is staged Ia–IV (one-A to four) based on the TNM status.Staging is based on a knowledge of how the cancer develops, from the primary tumor, to the invasion of nearby organs and tissues, to distant spread or metastasis. Staging systems have evolved over time, and they continue to change as scientists learn more about cancer. Some staging systems cover many different types of cancer, while others focus on more specific cancers. The TNM (primary tumor, regional lymph nodes, distant metastasis) is the most common staging system for mesothelioma.Treatment options are often determined by the stage of mesothelioma a patient is in. There are three staging systems currently in use for pleural mesothelioma and each one measures somewhat different variables; peritoneal mesothelioma is not staged.

Some elements common to most staging systems are:

• Location of the primary tumor.
• Size and number of the tumors.
• Lymph node involvement.
• Cell type and tumor grade.
• Metastasis.

Many cancer registries, such as the National Cancer Institute's Surveillance, Epidemiology, and End Results Program (SEER) use summary staging, a system used for all types of cancer. Summary staging groups cancer into five main categories:

• In situ - cancer that is present only in the layer of cells in which it began.
• Localized - cancer that is limited to the organ in which it began with no evidence of spread.
• Regional - cancer that has spread from the primary site to nearby lymph nodes or organs.
• Distant - cancer that has spread from the primary site to distant lymph nodes or organs.
• Unknown - cases where not enough information exists to indicate stage.

Several types of testing may be used to help doctors determine stage, and to formulate a treatment plan.

• Physical examinations. The doctor examines the body by looking, feeling and listening to anything out of the ordinary.
• Imaging techniques. Procedures such as x-rays, CT scans, MRIs and PET scans may show the location, size of the tumor and whether the cancer has spread.
• Laboratory tests. Studies of blood, urine, fluid and tissue can provide information about the cancer. Tumor markers, sometime elevated when cancer is present, may provide information.
• Pathology reports. Results of the examination of tissue samples can include information about the size of the tumor(s), extension into adjacent structures, type of cells and grade of the tumor. Results of the examination of cells in fluid, such as that from a mesothelioma-related pleural effusion, may also provide information.
• Surgical reports. Observations about the size and appearance of the tumor(s), lymph nodes and nearby organs.

Staging information should be provided to the patient by his doctor so that potential treatment plans can be discussed. Stage of the mesothelioma, as well as consideration of other factors such as age, health status and the patient's wishes may dictate different treatment options.

The oldest staging system and the one most often used is the Butchart System which is based mainly on the extent of primary tumor mass and divides mesotheliomas into four stages. The more recent TNM system considers variables of tumor in mass and spread, lymph node involvement, and metastasis. The Brigham System is the latest system and 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

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