Malignant mesotheliomas are staged surgically as follows:
Stage 1–tumor confined to one hemithorax or to the peritoneal cavity Stage 2–tumor involving the chest wall: mediastinum, pericardium, or the contra-lateral pleura. Stage 3–tumor in both thorax and abdomen or in lymph nodes outside the chest Stage 4–distant bloodborne metastases.
While the extent of disease cannot be accurately delineated on a flat chest film, the characteristic orange-peel appearance and mediastinal involvement can frequently be seen clearly on CT scan. The CT scan is used increasingly for staging.
Mesothelioma encases the lung, preventing proper expansion, but direct invasion of the lungs is not usually encountered. In early stage 1, the peel is relatively thin, and it is sometimes possible merely to peel the pleura from the lung without doing a pneumonectomy.
More extensive resection is usually necessary with a thicker tumor. Beyond stage 1, the tumor is more difficult to resect, and the attempt is made only occasionally.
Mesothelioma is a highly malignant, almost invariably lethal tumor regardless of histologic type. Survival time appears to correlate with the stage of disease. But even patients with stage 1 disease–the majority–do not have a good prognosis. The typical mesothelioma survival rate with stage 1 or 2 disease generally die within two years.
Virtually the average mesothelioma patient with stage 3 disease are dead within one year, with a median survival of only six months. Almost half of patients have no known history of asbestos exposure; however, there is no correlation of exposure or site of the primary lesion with prognosis.
In general, the longer the duration of symptoms before diagnosis, the better the prognosis–that is, indolent tumors remain slow growing. Degree of dyspnea is apparently dependent upon the amount of pleural effusion, in addition to tumor volume; a small amount of tumor may be associated with a large pleural effusion. The degree of pain appears to be related to invasion of the chest wall, denoting a more aggressive tumor.
The most frequent cause of death from mesothelioma is respiratory failure, mainly because the disease in almost half of patients remains localized to the chest. Pleural mesothelioma is bilateral at presentation in fewer than 5 percent of patients. Spread to the opposite lung or into the abdomen–bowel obstruction also may be a cause of death–does not usually occur until late in the disease course.
Small bowel obstruction is the most frequent cause of death resulting from primary peritoneal mesotheliomas. Patients with pericardial or cardiac involvement may die of arrhythmia, congestive heart failure, or, if vessels are compromised, a myocardial infarct.