- Oral cavity SCC is staged using the AJCC 8th edition TNM system:
- Which uniquely incorporates:
- Depth of invasion (DOI) into the T classification and extranodal extension (ENE) into the N classification:
- Two major changes from prior editions
- Depth of invasion (DOI) into the T classification and extranodal extension (ENE) into the N classification:
- Which uniquely incorporates:
- The following summarizes the complete staging system per the NCCN Head and Neck Cancer Guidelines
- Primary Tumor (T) Classification:
- The T category is determined by both tumor size and DOI (measured from the basement membrane of adjacent normal mucosa, not tumor thickness):
- Tis — Carcinoma in situ
- T1 — Tumor ≤2 cm, DOI ≤5 mm
- T2 — Tumor ≤2 cm with DOI >5 mm, OR tumor >2 cm and ≤4 cm with DOI ≤10 mm
- T3 — Tumor >2 cm and ≤4 cm with DOI >10 mm, OR tumor >4 cm with DOI ≤10 mm
- T4a — Tumor >4 cm with DOI >10 mm, OR invasion of adjacent structures (through cortical bone of mandible/maxilla, maxillary sinus, skin of face):
- Superficial erosion of bone/tooth socket alone by a gingival primary does not qualify
- T4b — Invasion of masticator space, pterygoid plates, skull base, and/or encasement of internal carotid artery
- The T category is determined by both tumor size and DOI (measured from the basement membrane of adjacent normal mucosa, not tumor thickness):
- Regional Lymph Nodes (N) — Clinical (cN):
- N0 — No regional lymph node metastasis
- N1 — Single ipsilateral node ≤3 cm, ENE(−)
- N2a — Single ipsilateral node >3 cm but ≤6 cm, ENE(−)
- N2b — Multiple ipsilateral nodes, none >6 cm, ENE(−)
- N2c — Bilateral or contralateral nodes, none >6 cm, ENE(−)
- N3a — Any node >6 cm, ENE(−)
- N3b — Any node(s) with clinically overt ENE(+)
- Regional Lymph Nodes (N) — Pathological (pN):
- The key difference from clinical N staging is that ENE now upstages nodal disease:
- pN1 — Single ipsilateral node ≤3 cm, ENE(−)
- pN2a — Single ipsilateral node ≤3 cm with ENE(+), OR single ipsilateral node >3–6 cm and ENE(−)
- pN2b — Multiple ipsilateral nodes, none >6 cm, ENE(−)
- pN2c — Bilateral/contralateral nodes, none >6 cm, ENE(−)
- pN3a — Any node >6 cm, ENE(−)
- pN3b — Single ipsilateral node >3 cm with ENE(+), OR multiple nodes any with ENE(+), OR single contralateral node of any size with ENE(+)
- The key difference from clinical N staging is that ENE now upstages nodal disease:
- Key Points on the 8th Edition Changes
DOI vs. tumor thickness:- DOI is measured from the horizon of the basement membrane of adjacent uninvolved mucosa perpendicularly to the deepest point of invasion — distinct from tumor thickness, which is measured from the surface:
- For every 5 mm increase in DOI, the T category increases by one level (cutoffs at 5 mm and 10 mm)
- Upstaging impact:
- Incorporation of DOI led to upstaging of approximately:
- 29% to 36% of patients in the T category
- ENE led to upstaging in:
- ~13% for the N category
- Incorporation of DOI led to upstaging of approximately:
- The 8th edition demonstrates improved prognostic discrimination compared to the 7th edition (Harrell’s C-index 0.70–0.74 vs. 0.65–0.69 for OS and DSS)
- Clinical implications:
- Patients with small tumors (formerly T1) upstaged to T3 based on DOI >10 mm may benefit from postoperative radiotherapy, even in the N0 setting
- DOI is an independent predictor of regional nodal metastasis and disease-specific survival
- DOI is measured from the horizon of the basement membrane of adjacent uninvolved mucosa perpendicularly to the deepest point of invasion — distinct from tumor thickness, which is measured from the surface:
Rodrigo Arrangoiz MS, MD, FACS, FSSO 