Table 2. Classification criteria of TNM 6th and TNM 7th staging system for nasopharyngeal carcinoma.

	TM6th	TNM7th
T classification
T1	nasopharynx	nasopharynx, oropharynx or nasal cavity
T2
T2a	oropharynx and/or nasal cavity	pharapharyneal extension
T2b	parapharyneal extension
T3	bony structures and/or paranasal sinuses	bony structures and/or paranasal sinuses
T4	intracranial extension and/or cranial nerves, infratemporal fossa hypophaynx, orbit or masticatory spacea	intracranial extension and/or cranial nerves, hypopharynx, orbit or infratemporal fossa/masticatory spaceb
N classification
N0	none	none
N1	unilateral node(s), ≤6cm in greatest dimension, above the supraclavicular fossa	unilateral cervical and/or unilateral or bilateral retropharyngeal node(s),≤6cm in greatest dimension, above the supraclavicular fossa
N2	bilateral node(s),≤6cm in greatest dimension, above the supraclavicular fossa	bilateral cervical node(s),≤6cm in greatest dimension, above the supraclavicular fossa
N3a	>6cm, or in supraclavical fossa	>6cm, or in supraclavical fossa
stage group
I	T1N0M0	T1N0M0
II		T1N1M0, T2N0-1M0
IIA	T2aN0M0
IIB	T1-2aN1M0, T2bN0-1M0
III	T1-2bN2M0, T3N0-2M0	T1-2N2M0, T3N0-2M0
IVA	T4N0-2M0	T4N0-2M0
IVB	any T N3M0	any T N3M0
IVC	any T any N 3M1	any T any N 3M1

Abbreviations: UICC = the International Union Against Cancer; AJCC  =  American Joint Committee on Cancer

^aMasticator space involvement denotes extension of tumor beyond the anterior surface of the lateral pterygoid muscle or lateral extension beyond the posterolateral wall of the maxillary antrum and the pterygomaxillary fissrue.

^bMasticator space primarily consists of the muscles of mastication. Anatomically, the superficial layer of the deep cervical fascia splits to enclose the muscles of mastication to enclose this space. These muscles are the medial and lateral pterygoid, masseter and temporalis.