Table 1.

TNM classification according to WHO.

T – Primary tumor size	Tx primary tumor cannot be assessed
	T0 no evidence of primary tumor
	Tis carcinoma in situ
	T1 tumor 2 cm or less in the largest dimension
	T2 tumor larger than 2 cm but smaller than 4 cm in the largest dimension
	T3 tumor larger than 4 cm in the largest dimension
	T4a (lip) tumor invades the cortical bone, inferior alveolar nerve, floor of the mouth or skin (chin or nose)
	T4a (oral cavity) tumor invades the cortical bone, into deep/extrinsic muscles of the tongue (genioglossus, hyoglossus, palatoglossus, and styloglossus), maxillary sinus or skin of the face
	T4b (lip and oral cavity) tumor invades the masticator space, pterygoid plates, or skull base; or encases internal carotid artery Note: Superficial erosions of the bone/tooth socket alone; or a primary tumor of the gums, are not sufficient to classify a tumor as T4
N –Regional lymph nodes	Nx regional lymph nodes cannot be assessed
	N0 no regional lymph node metastasis
	N1 metastasis in a single ipsilateral lymph node, 3 cm or smaller in the largest dimension
	N2 N2a metastasis in a single ipsilateral lymph node, larger than 3 cm but smaller than 6 cm in the largest dimension N2b metastasis in multiple ipsilateral lymph nodes, none larger than 6 cm in the largest dimension N2c metastasis in bilateral or contralateral lymph nodes, none larger than 6 cm in the largest dimension
	N3 metastasis in a lymph node larger than 6 cm in the largest dimension Note: Mid-line nodes are considered as ipsilateral nodes
M – Distant metastasis	Mx distant metastasis cannot be assessed
	M0 no distant metastasis
	M1 distant metastasis