After mesothelioma is diagnosed, the stage of the cancer is determined by various tests, including X-ray and other forms of imaging where the doctor can see the tumor and how it has spread inside the body.1 Mesothelioma staging is for pleural mesothelioma specifically, the most common type of malignant mesothelioma. There are no accepted guidelines for staging of peritoneal mesothelioma or the other rare forms of the disease.2
The National Cancer Institute1 in the United States uses Roman numerals (I-IV) to refer to the stages, but in other parts of the world Arabic numbers (1-4) are used.2 Both systems have similar definitions for the stages.
Stage I malignant mesothelioma is also known as localized cancer and is divided into two stages:
- Stage IA — The cancer is found on only one side of the chest and has not yet grown on the lining of the lung; it is only found along the lining of the chest wall or between the chest and the lining of the lung or diaphragm.
- Stage IB — Same as stage IA but involves the lining of the lung.
Stages II, III and IV mesothelioma are considered advanced mesothelioma because the disease has spread from the original tumor.
In stage II mesothelioma, the cancer is still only on one side of the chest, but it has spread from the lining of the chest wall to include both layers of the lining of the lungs, known as the pleura, and into either the diaphragm or the lung itself.
Stage III mesothelioma describes two different possible ways that the disease can spread:
- The cancer is still only on one side of the chest but has spread to nearby lymph nodes
- The cancer spreads to the lining around the heart, between the ribs, the soft tissues in the chest cavity or the fatty tissue between the lungs
Stage IV mesothelioma describes a metastatic mesothelioma — spread of the cancer to other organs and areas of the body. Malignant mesothelioma can spread to the lymph nodes, peritoneum (abdomen), other side of the chest cavity, internal organs or more distant sites like the spine and brain.
Peritoneal mesothelioma staging
Most cancers are staged based on a universal system known as TNM. With the lack of a staging system like the one above for pleural mesothelioma, doctors rely on the TNM classification to grade a peritoneal mesothelioma cancer.2 Increasing "T" numbers (0-4) refer to the size of the original tumor (called the primary tumor). The "N" refers to the spread of mesothelioma to the lymph nodes, and "M" represents spread to another part of the body (metastasis). Increasing numbers indicate greater spread.3
Diagnosis at earlier stages increases the odds of survival, and knowing the stage of the cancer can help doctors plan treatments.