This is also sometimes called the International Mesothelioma Interest Group staging system. The TNM system describes the extent of the primary tumor (T), the absence or presence of cancer in nearby lymph nodes (N), and the absence or presence of distant metastases (M). Once the TNM categories have been decided, this information is grouped together to give the stage. Stage 1 is the earliest stage and stage 4 is the most advanced stage.

Stage I :

Mesothelioma affects one layer of the pleura only. It may have grown into pericardium and the diaphragm

Stage II :

Mesothelioma has spread to both layers of the pleura on one side of the body only

Stage III :

Mesothelioma has spread to the chest wall, food pipe or lymph nodes on the same side of the chest

Stage IV :

Mesothelioma has spread via the bloodstream to other organs in the body such as the liver, brain or bone or to lymph nodes on the other side of the chest.