Stage IV includes: IVA: (Any T, Any N, M1a); (Any T, Any N, M1b); IVB: (Any T, Any N, M1c). M1a: Tumor with separate tumor nodule(s) in a contralateral lobe; tumor with pleural or pericardial nodules or malignant pleural or pericardial effusion. Most pleural (pericardial) effusions with lung cancer are a result of the tumor. In a few patients, however, multiple microscopic examinations of pleural (pericardial) fluid are negative for tumor, and the fluid is nonbloody and not an exudate. If these elements and clinical judgment dictate that the effusion is not related to the tumor, the effusion should be excluded as a staging descriptor. M1b: Tumor with single extrathoracic metastasis in a single organ (including involvement of a single nonregional node). M1c: Tumor with multiple extrathoracic metastases in a single organ or in multiple organs. (AJCC 8th ed.) [from NCI]