Stage IV includes: IVA (T4a, N0, M0); (T4a, N1, M0); (T0, N2, M0); (T1, N2, M0); (T2, N2, M0); (T3, N2, M0); (T4a, N2, M0); IVB (T4b, Any N, M0); (Any T, N3, M0); IVC (Any T, Any N, M1). T4a: Moderately advanced disease. Tumor invades skin, mandible, ear canal, and/or facial nerve. T0: No evidence of primary tumor. T1: Tumor measuring 2 cm or less in greatest dimension without extraparenchymal extension. T2: Tumor measuring more than 2 cm, but not more than 4 cm in greatest dimension without extraparenchymal extension. T3: Tumor measuring more than 4 cm in greatest dimension, and/or tumor having extraparenchymal extension. T4b: Very advanced disease. Tumor invades skull base and/or pterygoid plates and/or encases carotid artery. N0: No regional lymph node metastasis. N1: Metastasis in a single ipsilateral lymph node, 3 cm or less in greatest dimension. N2: Metastasis in a single ipsilateral lymph node, 3 cm or less in greatest dimension and ENE(+); or more than 3 cm but not more than 6 cm in greatest dimension and ENE(-); or metastases in multiple ipsilateral lymph nodes, none more than 6 cm in greatest dimension and ENE(-), or in bilateral or contralateral lymph nodes, none more than 6 cm in greatest dimension and ENE(-). N3: Metastasis in a lymph node larger than 6 cm in greatest dimension and ENE(-); or in a single ipsilateral node larger than 3 cm in greatest dimension and ENE(+); or multiple ipsilateral, contralateral, or bilateral nodes any with ENE(+). M0: No distant metastasis. M1: Distant metastasis. (AJCC 8th ed.) [from NCI]