Nasopharynx

Nasopharyngeal carcinoma (NPC) is an uncommon malignancy that is more frequently seen in the Inuit population as well as the ethnic Chinese population particularly from the Guangdong province.¹
This increased risk is thought to be due to a combination of genetic and environmental factors.
Environmental factors that are associated with NPC include salted fish (thought to be related to nitrosamines) and Epstein-Barr virus (EBV) infection.

Pathologically, the most recent World Health Organization (WHO) Classification of Tumours (4th Edition, 2017) has divided NPC into the following groups:²

T0 has been added to the classification system for situations where there is EBV positive metastatic carcinoma of unknown primary.
References to the masticator space and infratemporal fossa have been removed and replaced with consistent definitions that refer to specific soft tissue and bony structures.

Retropharyngeal nodal involvement (unilateral or bilateral) is now clearly N1.
Subcategories within N3 (N3a, N3b) have now been eliminated.
Involvement supraclavicular fossa have been removed as a criterion for N3 disease. Instead, the inferior border of the cricoid cartilage is used as a demarcating point.

T Category	Criteria
TX	Primary tumour cannot be assessed
T0	No primary tumour identified, but EBV positive cervical nodal involvement.
Tis	Carcinoma in situ.
T1	Tumour involving the nasopharynx +/- nasal cavity +/- oropharynx without involvement of the parapharyngeal space
T2	Extension to the parapharyngeal space. OR involvement of surrounding soft tissue structures (medial pterygoid muscle, lateral pterygoid muscle, prevertebral muscles).
T3	Tumour involvement of bony structures (medial or lateral pterygoid plates, cervical vertebrae, skull base, paranasal sinuses).
T4	Tumor with intracranial extension, involvement of cranial nerves, hypopharynx, orbit, parotid gland, and/ or extensive soft tissue infiltration beyond the lateral surface of the lateral pterygoid muscle

Mucosal involvement only of the nasopharynx, nasal cavity, or oropharynx by NPC is considered T1.
Involvement of the parapharyngeal space or soft tissue structures (medial/lateral pterygoid muscle, prevertebral muscle) up-categorizes to T2
Involvement of bony structures (medial/lateral pterygoid plates, cervical vertebrae, skull base, paranasal sinuses) up-categorizes to T3
Extension beyond these structures (skull base, orbit, hypopharynx, etc) up-categorizes to T4
Previously the AJCC 7^th edition guidelines referenced the infratemporal fossa (which has mainly bony limits) and the masticator space (which has fascial limits) in their staging. This had been confusing as the two areas are similar but not identical.

N Category	Criteria
NX	Regional lymph nodes cannot be assessed.
N0	No regional lymph node metastasis.
N1	Unilateral or retropharyngeal nodal involvement that is ≤ 6 cm in maximal dimension and above the caudal border of the cricoid cartilage.
N2	Bilateral nodal involvement that is ≤ 6 cm in maximal dimension and above the caudal border of the cricoid cartilage.
N3	Nodal involvement that is >6 cm in maximal dimension. OR nodal involvement that extends below the caudal border of the cricoid cartilage.

Unilateral or retropharyngeal nodal involvement up-categorizes to N1
Bilateral nodal involvement up-categorizes to N2
If there is any nodal involvement > 6 cm or nodes that extend below the caudal border of the cricoid then this is categorized as N3.

M Category	Criteria
M0	No distant metastasis
M1	Distant metastasis present

Bailey, B. J., Johnson, J. T., & Rosen, C. A. (2014). Chapter 120 – Nasopharyngeal Carcinoma. In Bailey's Otolaryngology – Head & Neck Surgery. Wolters Kluwer, Lippincott Williams et Wilkins. ↩
Grandis, El-Naggar AK Chan JK, and JR Takata T. Slootweg PJ WHO. "Classification of Head and Neck Tumours." (2017). ↩