What are the implications of the revised N staging system for surgery?
Malignant pleural mesothelioma has a poor prognosis and an average survival of 12–18 months despite treatment. One of the unique features of this malignancy is development of diffuse nodules inside the pleural cavity which lead to an irregular lymph node metastasis pattern in the chest cavity. Lymph node staging of mesothelioma was the same as Lung Cancer lymph node staging. It was recently revised to include unique intrathoracic involvement sites (internal mammary, peridiaphragmatic, pericardial fat pad and intercostal lymph nodes) in mesothelioma and ipsilateral mediastinal and intrapulmonary lymph nodes were grouped as N1. The preoperative invasive lymph node staging is inadequate and almost 40% are understaged in clinical N0 patients and 30% in N1 patients. Invasive mediastinal staging with cervical mediastinoscopy, endobronchial ultrasound or endoscopic ultrasound are used, however pericardial, posterior intercostal and internal mammary lymph nodes are inaccessible. Invasive preoperative mediastinal staging is important to stratify patients for appropriate treatment. The number and sites of potential lymph node involvement in mesothelioma is much higher and widespread than lung cancer. Thus, the technique and principles of lymphadenectomy or sampling in lung cancer is obviously not enough in mesothelioma. Long term survival difference is less than 10% in patients with bronchopulmonary or ipsilateral mediastinal and extrapleural lymph node involvement compared with those without lymph node involvement. The revised N staging system emphasizes the importance of preoperative invasive mediastinal staging, broadens surgical indications without dramatic improvements in survival.