TNM Staging of Oral Cavity Cancer
The TNM staging system for oral cavity cancer follows the AJCC 8th edition (effective 2018), which classifies tumors based on size, depth of invasion (DOI), nodal involvement, and distant metastases, with stage I-II representing early disease (small tumors without nodal involvement) and stage III-IV representing advanced disease (larger tumors with potential invasion of structures and/or nodal spread). 1
Anatomic Subsites of the Oral Cavity
The oral cavity includes the following subsites 1:
- Buccal mucosa
- Upper and lower alveolar ridge
- Retromolar trigone
- Floor of the mouth
- Hard palate
- Anterior two-thirds of the tongue (oral tongue)
Primary Tumor (T) Classification
The T classification for oral cavity cancer incorporates both tumor size and depth of invasion (DOI), a critical addition in the 8th edition 2:
- T1: Tumor ≤2 cm with DOI ≤5 mm 3
- T2: Tumor ≤2 cm with DOI >5 mm and ≤10 mm, OR tumor >2 cm but ≤4 cm with DOI ≤10 mm 3
- T3: Tumor >2 cm with DOI >10 mm, OR tumor >4 cm with DOI ≤10 mm 3
- T4a (moderately advanced): Tumor invades adjacent structures (e.g., through cortical bone, involves maxillary sinus, skin of face) 4
- T4b (very advanced): Tumor invades masticator space, pterygoid plates, skull base, or encases the carotid artery 4
The depth of invasion (DOI) is measured from the level of the basement membrane of the closest adjacent normal mucosa to the deepest point of tumor invasion and must be documented by pathologists as it critically determines T classification. 2
Regional Lymph Node (N) Classification
The N classification for oral cavity cancer is uniform across head and neck sites 1:
- N0: No regional lymph node metastasis 4
- N1: Metastasis in a single ipsilateral lymph node ≤3 cm in greatest dimension 4
- N2a: Single ipsilateral lymph node >3 cm but ≤6 cm 3
- N2b: Multiple ipsilateral lymph nodes, none >6 cm 1
- N2c: Bilateral or contralateral lymph nodes, none >6 cm 1
- N3: Lymph node(s) >6 cm 1
Extranodal extension (ENE) is a critical pathological feature that significantly impacts prognosis and treatment decisions, particularly regarding the need for adjuvant chemoradiation. 2
Distant Metastasis (M) Classification
Stage Grouping
The stage grouping combines T, N, and M classifications 4, 3:
- Stage I: T1N0M0
- Stage II: T2N0M0
- Stage III: T3N0M0 OR T1-3N1M0
- Stage IVA (moderately advanced): T4aN0-1M0 OR T1-4aN2M0
- Stage IVB (very advanced): T4b (any N) M0 OR any T with N3M0
- Stage IVC (distant metastatic): Any T, any N, M1
The terminology shift from "resectable/unresectable" to "moderately advanced/very advanced" for T4 lesions reflects that many anatomically resectable tumors are now treated nonsurgically with chemoradiation, and surgical feasibility depends on medical contraindications and anticipated functional outcomes, not just anatomic resectability. 1
Critical Prognostic Features
Beyond TNM staging, several pathological features significantly impact prognosis and treatment decisions 1:
- Extracapsular nodal spread: Category 1 indication for postoperative chemoradiation
- Positive mucosal margins: Category 1 indication for postoperative chemoradiation or reexcision
- Lymphovascular invasion: Important prognostic feature requiring documentation 3
- Perineural invasion: Risk feature for consideration of adjuvant therapy 1
- Nodal disease in levels IV or V: Risk feature for consideration of adjuvant therapy 1
Regional Lymphatic Drainage Patterns
The oral cavity has rich lymphatic supply with initial regional node dissemination to nodal groups at levels I through III, though the risk of nodal involvement varies significantly by subsite. 1
- High-risk subsites: Anterior tongue (50-60% occult metastasis rate) 1
- Low-risk subsites: Alveolar ridge and hard palate (infrequent neck involvement) 1
- Overall presentation: Approximately 30% of patients have regional node involvement at diagnosis 1
Clinical Implications
Stage at diagnosis predicts survival rates and guides management, with more advanced TNM stages associated with worse survival, though stage IV disease without distant metastases does not automatically mean incurable disease and can be treated with curative intent using aggressive combined modality therapy. 1, 3