Stage IV includes: IVA (T4a, N0, M0); (T4a, N1, M0); (T1, N2, M0); (T2, N2, M0); (T3, N2, M0); (T4a, N2, M0); IVB (Any T, N3, M0); (T4b, Any N, M0); IVC (Any T, Any N, M1). T4a (lip): Tumor invades through cortical bone, inferior alveolar nerve, floor of mouth, or skin of face, i.e., chin or nose. T4a (oral cavity): Tumor invades adjacent structures (e.g., through cortical bone, into deep [extrinsic] muscles of tongue, maxillary sinus, skin of face). T4b: Tumor invades masticator space, pterygoid plates, or skull base and/or encases internal carotid artery. 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. N2a: Metastasis in a single ipsilateral lymph node more than 3 cm but not more than 6 cm in dimension. N2b: Metastasis in multiple ipsilateral lymph nodes, none more than 6 cm in greatest dimension. N2c: Metastasis 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. M1: Distant metastasis. (AJCC 6th and 7th eds.) [from NCI]