Stage IV includes: IVA: (Any T, N1, M0); (Any T, N0,1, M1a); IVB: (Any T, N2, M0, M1a); (Any T, Any N, M1b). N0: No regional lymph node metastasis. N1: Metastasis in anterior (perithymic) lymph nodes. N2: Metastasis in deep intrathoracic or cervical lymph nodes. M0: No distant metastasis. M1a: Separate pleural or pericardial nodule(s). M1b: Pulmonary intraparenchymal nodule or distant organ metastasis. (AJCC 8th ed.) [from NCI]