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.
  

quoted from "http://www.mesotheliomaweb.org/symptoms.htm"