Stage IV includes: IVA (T4a, N0, M0); (T4a, N1, 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. T1: Tumor measuring 2 cm or less in greatest dimension without extraparenchymal extension. Extraparenchymal extension is clinical or macroscopic evidence of invasion of soft tissues. Microscopic evidence alone does not constitute extraparenchymal extension for classification purposes. 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, more than 3 cm but not more than 6 cm in greatest dimension, or in multiple ipsilateral lymph nodes, none more than 6 cm in greatest dimension, or in bilateral or contralateral lymph nodes, none more than 6 cm in greatest dimension. N3: Metastasis in a lymph node, more than 6 cm in greatest dimension. M0: No distant metastasis. M1: Distant metastasis. (AJCC 7th ed.) [from NCI]