Table 1.
Summary of tumour classification systems AJCC 8th edition and BWH.
| AJCC-8 Classification | BWH Classification | ||
|---|---|---|---|
| Primary tumour (T) | |||
| T1 | Tumour < 2 cm in greatest dimension | T1 | 0 high-risk factors b |
| T2 | Tumour ≥ 2 cm and <4 cm in greatest dimension | T2a | 1 high-risk factor |
| T3 | Tumour ≥ 4 cm in greatest dimension or minor bone erosion or PNI or deep invasion a | T2b | 2–3 high-risk factors |
| T4a | Tumour with gross cortical bone/marrow invasion | T3 | 4 high-risk factors or bone invasion |
| T4b | Tumour with axial skeleton invasion including foraminal involvement and vertebral foramen involvement to the epidural space | ||
| Regional lymph nodes (N) | |||
| Nx | Regional lymph nodes cannot be assessed | ||
| N1 | Metastasis in a single ipsilateral lymph node ≤3 cm in greatest dimension and ENE (−) | ||
| N2a | Metastasis in a single ipsilateral lymph node >3 cm and ≤6 cm in greatest dimension and ENE (−) | ||
| N2b | Metastasis in multiple ipsilateral nodes all ≤6 cm in greatest dimension and ENE (−) | ||
| N2c | Metastasis in bilateral or contralateral lymph node(s), all ≤6 cm in greatest dimension and ENE (−) | ||
| N3a | Metastasis in a lymph node >6 cm in greatest dimension and ENE (−) | ||
| N3b | Metastasis in any lymph node(s) and ENE (+) | ||
| Distant metastasis (M) | |||
| M0 | No distant metastasis | ||
| M1 | Distant metastasis | ||
AJCC, American Joint Committee on Cancer; BWH, Brigham and Women’s Hospital; ENE, extranodal extension; PNI, perineural invasion. a Deep invasion defined as invasion beyond the subcutaneous fat or >6 mm (as measured from the granular layer of adjacent normal epidermis to the base of the tumour); perineural invasion for T3 classification is defined as tumour cells within the nerve sheath of a nerve lying deeper than the dermis or measuring 0.1 mm or larger in calibre or presenting with clinical or radiographic involvement of tumour named nerves without skull base invasion or transgression [19]. b Risk factors include tumour diameter 2 cm or larger, poorly differentiated histology, perineural invasion, and tumour invasion beyond the subcutaneous fat (excluding bone, which automatically upgrades to T3) [20].