Malignant pleural mesothelioma

Despite innumerable trials of surgery, radiotherapy, and countless chemotherapeutic drugs, it is unclear whether any intervention has had a significant impact on more than a few highly selected patients with malignant pleural mesothelioma. Because most patients die of respiratory failure from extensive disease progression in the thorax, treatment usually includes attempts at local control. Unfortunately, radiotherapy is associated with significant complications in pleural mesothelioma, and surgery is feasible in only a small percentage of patients. Although there have been several single-institution reports of combined-modality therapy with extrapleural pneumonectomy, postoperative radiation, and chemotherapy in which prolonged survival has been observed, most patients with malignant pleural mesothelioma have locally advanced disease, advanced age, or comorbid medical illnesses that preclude aggressive surgery. Therefore, the use of a systemic anticancer agent is the only treatment option for most patients with malignant pleural mesothelioma. Evaluation of effective chemotherapy regimens for this disease has been hampered by many factors. Because mesothelioma is an uncommon malignancy, most studies have enrolled small numbers of patients, and few trials have been randomized. The disease is heterogeneous, yet until recently there was no single staging system that could reliably predict survival, nor is there a universally accepted set of prognostic criteria for selecting a uniform group of patients. Response assessment has been limited by the inherent difficulties of reproducibly measuring pleural-based disease. The real impact of systemic chemotherapy on the natural history of malignant mesothelioma is still uncertain because phase III trials comparing chemotherapy with best supportive care have not yet been completed. Although nearly every class of cytotoxic agent has been evaluated in mesothelioma, response rates of greater than 20% have not been consistently demonstrated for any drug. The most active drug classes are the antifolates, the anthracyclines, and the platinums. Doxorubicin has historically been considered the gold-standard chemotherapy, although its true response rate is likely only 15%. The most active commercially available drug for mesothelioma so far appears to be gemcitabine. Although gemcitabine has a limited role as a single agent, it is quite active in combination with a platinating agent. The impressive 48% response rate reported for the combination of gemcitabine with cisplatin in a single phase II study has made this regimen the new standard of care for off-protocol treatment of this disease, although this trial still requires validation. With the recent introduction of several new agents with definite activity in this disease, the therapeutic nihilism previously associated with malignant pleural mesothelioma is gradually being replaced by a cautious optimism. Early trials of angiogenesis inhibitors, gene therapy, and vaccines offer additional avenues for treatment. As we begin to incorporate these active new drugs with each other and in adjuvant and neoadjuvant treatment regimens, there is reason to believe that superior results for patients with malignant pleural mesothelioma can be achieved in the near future.