Oropharynx (p16-)

The AJCC 8^th Edition Guidelines now separately stage p16- oropharyngeal carcinoma from p16+ (HPV associated) oropharyngeal carcinoma.
The T0 category has been removed for p16 negative OPSCC.
- The T0 classification only remains when the primary site of a metastatic node can be identified pathologically (such as if it were p16+ or EBV positive, as this would suggest an oropharyngeal or nasopharyngeal primary site respectively).
p16- oropharyngeal carcinoma continues to use the standard shared nodal staging and group staging as in previous editions
However, the shared N-Categorization has now been changed to factor in extranodal extension.

T Category	Criteria
TX	Primary tumour cannot be assessed
Tis	Carcinoma in situ.
T1	2 cm or smaller in greatest dimension.
T2	> 2 cm - 4 cm in greatest dimension
T3	> 4 cm in greatest dimension. OR extension to the lingual surface of the epiglottis.
T4	Moderately advanced (T4a) or very advanced (T4b) disease
T4a	Moderately advanced local disease Tumour invasion of the larynx, extrinsic muscles of the tongue, medial pterygoid, hard palate, or mandible Tumour extension to the lingual surface of the epiglottis does not constitute invasion of the larynx (would be classified as T3 instead as above).
T4b	Very advanced local disease Tumour invasion of the lateral pterygoid, pterygoid plates, lateral nasopharynx, skull base, or carotid artery encasement.

T1, T2, and T3 are determined by size thresholds of 2 cm or less, > 2 - 4 cm, and > 4 cm.
The presence of mucosal extension to the lingual surface of the epiglottis up-categorizes to T3 but not T4, however any other laryngeal invasion up-categorizes to T4b.
Involvement of the medial pterygoid muscle up-categorizes to T4a.
Involvement of the lateral pterygoid muscle up-categorizes to T4b.
Involvement of the pterygoid plates up-categorizes to T4b.
The palatoglossus is an extrinsic muscle of the tongue but is also within the oropharynx itself. As a result, involvement of the palatoglossus within the oropharynx does not denote a significantly poorer prognosis and does not change the T category.

N Category	Criteria
NX	Regional lymph nodes cannot be assessed.
N0	No regional lymph node metastasis.
N1	Single ipsilateral lymph node that is 3 cm or less in maximal dimension without extranodal extension
N2
N2a	Single ipsilateral lymph node that is > 3 cm but ≤ 6 cm in maximal dimension without extranodal extension
N2b	Mulple ipsilateral lymph nodes that are ≤ 6 cm in maximal dimension without extranodal extension
N2c	Bilateral or contralateral lymph nodes that are ≤ 6 cm in maximal dimension without extranodal extension
N3
N3a	Metastasis in any lymph node > 6 cm without extranodal extension
N3b	Metastasis in any lymph node with clinically overt *extranodal extension.*

N Category	Criteria
NX	Regional lymph nodes cannot be assessed.
N0	No regional lymph node metastasis.
N1	Single ipsilateral lymph node that is 3 cm or less in maximal dimension without extranodal extension
N2
N2a	Single ipsilateral lymph node that is > 3 cm but ≤ 6 cm in maximal dimension without extranodal extension
	OR metastasis to a single ipsilateral lymph node that is 3 cm or less in maximal dimension *WITH extranodal extension*
N2b	Mulple ipsilateral lymph nodes that are ≤ 6 cm in maximal dimension without extranodal extension
N2c	Bilateral or contralateral lymph nodes that are ≤ 6 cm in maximal dimension without extranodal extension
N3
N3a	Metastasis in any lymph node > 6 cm without extranodal extension
N3b	Metastasis in any lymph node with clinically overt *extranodal extension.*
	*EXCEPT* if it a single ipsilateral node that is 3 cm or less with extranodal (which would instead be categorized as N2a as above).

Uses the Shared Nodal Staging System described previously.
If a patient has any clinical extranodal extension, they are automatically be categorized in the maximum possible N sub-category (N3b).
Pathologic N categorization is almost the same except for the isolated situation of having a single ipsilateral lymph node that is 3 cm or less with ENE identified only on pathology.
- Instead of being up-categorized to N3b, this specific case is up-categorized to N2a instead.
- In all other situations where there is ENE (clinical or pathologic), they are still up-categorized to N3b.
Clinically the AJCC defines ENE as invasion of skin, infiltration of musculature/fixation to adjacent structures on clinical examination, cranial nerve, brachial plexus, sympathetic trunk or phrenic nerve invasion with dysfunction.

Pathologically, ENE is defined as extension of metastatic tumour beyond the confines of the lymph node itself.
Clinically the AJCC defines ENE as invasion of skin, infiltration of musculature/fixation to adjacent structures on clinical examination, cranial nerve, brachial plexus, sympathetic trunk or phrenic nerve invasion with dysfunction.

M Category	Criteria
M0	No distant metastasis
M1	Distant metastasis present

Uses the Shared Group Staging System described previously.
Straightforward to remember due to the pattern seen above when creating a table against the T and N staging.
(T1 N0) is staged as Stage I, and (T2, N0) is staged as Stage II. Thereafter, each increasing stage is immediately to the right and below the previous stage.