[The 9th TNM classification of thoracic tumors]

The TNM classification applies to three types of thoracic tumors: lung cancer, thymic epithelial tumors (thymomas, neuroendocrine neoplasms, carcinomas), and pleural mesotheliomas. This 9th edition introduces two changes for the lung: category N2 (mediastinal lymph node metastases) is divided into N2a and N2b, when one N2 station or several N2 stations are affected, respectively, regardless of the number of lymph nodes; category M1c (multiple extrathoracic metastases) is divided into M1c1 and M1c2 when multiple extrathoracic metastases are present in one or more organs, respectively. There are no changes for category T. With regard to the thymus, the changes only concern the T descriptor with the introduction of size: T1a represents tumors ≤5cm and T1b tumors >5cm; and the invasion of the lung parenchyma and phrenic nerve becomes T2, which also includes invasion of the pericardium. Invasion of the mediastinal pleura is no longer a TNM criterion and is considered as an additional histological parameter. Regarding pleural mesotheliomas, as curative surgical resection is exceptional, the proposed changes only involve the clinical T descriptor, with no change to the pathological T descriptor or the N and M descriptors. T is defined on CT scan and depends on the sum of the maximum thickness of the pleura measured on three axial sections at the upper, middle, and lower hemithorax levels, and on the maximum pleural thickness in the fissure on a sagittal section.