# N stage N stage The system for describing the anatomy of regional lymph node metastases has been well described previously and is outlined in Figure 53.3 . It divides the lateral neck nodes into five sepa - rate levels, based on their relationship to certain anatomical structures. SCC in the oral cavity and lips tends to metastasise to lymph nodes at levels I, II and III. However, with SCC of the or or oral tongue there is a risk of skip metastasis directly to lymph node levels III or IV , without the involvement of higher level lymph node groups. By contrast, tumours arising in the oro pharynx commonly metastasise to lymph node levels II–IV , as well as retropharyngeal and contralateral nodal groups. In addition to the number , size and location of involved nodes, ENE has now been included as a contributor to nodal staging ( Table 53.2 ). ENE has been reliably shown to be an adverse prognosticator in all oral cavity tumours. Joint Committee on Cancer (AJCC) tumour–node– metastasis (TNM) staging manual, 8th edition. T category T criteria TX Primary tumour cannot be assessed Tis Carcinoma in situ T1 Tumour ≤ 2 /uni00A0 cm, ≤ 5 /uni00A0 mm DOI T2 Tumour ≤ 2 /uni00A0 cm, DOI >5 /uni00A0 mm and ≤ 10 /uni00A0 mm tumour >2 /uni00A0 cm but ≤ 4 /uni00A0 cm, and ≤ 10 /uni00A0 mm DOI T3 Tumour >4 /uni00A0 cm any tumour >10 /uni00A0 mm DOI T4 Moderately advanced or very advanced local disease T4a Moderately advanced local disease: (lip) tumour invades through cortical bone or involves the inferior alveolar nerve, /f_l oor of mouth or skin of face (i.e. chin or nose); (oral cavity) tumour invades adjacent structures only (e.g. through cortical bone of the mandible or maxilla, or involves the maxillary sinus or skin of the face); note that super /f_i cial erosion of bone/tooth socket (alone) by a gingival primary is not suf /f_i cient to classify a tumour as T4 T4b Very advanced local disease; tumour invades masticator space, pterygoid plates or skull base and/or encases the internal carotid artery DOI, depth of invasion (not tumour thickness). Reproduced with permission from AJCC, Chicago, IL, USA. The original source for this material is the AJCC Cancer Staging Manual 8th edition (2017) published by Springer Science+Business Media LLC (springer.com) (Amin MB, Edge SB, Greene FL et al . (eds). AJCC cancer staging manual , 8th edn. New York, NY: Springer International Publishing: American Joint Commission on Cancer, 2017). N stage The system for describing the anatomy of regional lymph node metastases has been well described previously and is outlined in Figure 53.3 . It divides the lateral neck nodes into five sepa - rate levels, based on their relationship to certain anatomical structures. SCC in the oral cavity and lips tends to metastasise to lymph nodes at levels I, II and III. However, with SCC of the or or oral tongue there is a risk of skip metastasis directly to lymph node levels III or IV , without the involvement of higher level lymph node groups. By contrast, tumours arising in the oro pharynx commonly metastasise to lymph node levels II–IV , as well as retropharyngeal and contralateral nodal groups. In addition to the number , size and location of involved nodes, ENE has now been included as a contributor to nodal staging ( Table 53.2 ). ENE has been reliably shown to be an adverse prognosticator in all oral cavity tumours. Joint Committee on Cancer (AJCC) tumour–node– metastasis (TNM) staging manual, 8th edition. T category T criteria TX Primary tumour cannot be assessed Tis Carcinoma in situ T1 Tumour ≤ 2 /uni00A0 cm, ≤ 5 /uni00A0 mm DOI T2 Tumour ≤ 2 /uni00A0 cm, DOI >5 /uni00A0 mm and ≤ 10 /uni00A0 mm tumour >2 /uni00A0 cm but ≤ 4 /uni00A0 cm, and ≤ 10 /uni00A0 mm DOI T3 Tumour >4 /uni00A0 cm any tumour >10 /uni00A0 mm DOI T4 Moderately advanced or very advanced local disease T4a Moderately advanced local disease: (lip) tumour invades through cortical bone or involves the inferior alveolar nerve, /f_l oor of mouth or skin of face (i.e. chin or nose); (oral cavity) tumour invades adjacent structures only (e.g. through cortical bone of the mandible or maxilla, or involves the maxillary sinus or skin of the face); note that super /f_i cial erosion of bone/tooth socket (alone) by a gingival primary is not suf /f_i cient to classify a tumour as T4 T4b Very advanced local disease; tumour invades masticator space, pterygoid plates or skull base and/or encases the internal carotid artery DOI, depth of invasion (not tumour thickness). Reproduced with permission from AJCC, Chicago, IL, USA. The original source for this material is the AJCC Cancer Staging Manual 8th edition (2017) published by Springer Science+Business Media LLC (springer.com) (Amin MB, Edge SB, Greene FL et al . (eds). AJCC cancer staging manual , 8th edn. New York, NY: Springer International Publishing: American Joint Commission on Cancer, 2017).