Staging is the term used to describe the extent of a patient's cancer, based on the primary tumor and its spread in the body. It can help the medical team plan treatment, forecast possible prognosis, and identify clinical trials for which the patient may be eligible.

Staging is based on the 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 different staging systems are:

1-Summary staging: This type of staging is used by many cancer registries, make use of this type of staging. 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.

2-Butchart System : This is based on the extent of primary tumor mass and divides mesothelioma into four stages.

* Stage I: Tumor is present in the right or left pleura and may also involve the diaphragm on the same side.

* Stage II: Tumor 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: Tumor 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.

3-TNM System :This is the most widely used staging system . It uses variables of T (tumor), N (lymph nodes), M (metastasis)

* Stage I: Tumor 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: Tumor 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: Tumor 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: Tumor 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.

4-Brigham System: This is the latest system and stages mesothelioma according to resectability (the ability to surgically remove) and lymph node involvement.

* Stage I: Resectable tumor and no lymph node involvement

* Stage II: Resectable tumor but with lymph node involvement

* Stage III: Unresectable tumor extending into chest wall, heart, or through diaphragm, peritoneum; with or without extra thoracic lymph node involvement

* Stage IV: Distant metastatic disease

Knowing the stage of the mesothelioma cancer will then lead to the next step in management which is treatment.