Earliest staging system for mesothelioma Stage I Mesothelioma has affected the right or left side of the pleura (chest) cavity, and may also be seen in the diaphragm. Stage II Mesothelioma has penetrated the chest lining into the heart, pleura, or esophagus on both sides. Lymph nodes may be affected. Stage III Mesothelioma has reached the peritoneum (abdominal cavity). Lymph nodes past the chest may be affected. Stage IV Mesothelioma has entered the bloodstream and reached other organs