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Oral cavity cancer
Oral cavity cancer is squamous cell carcinoma treated first by surgery; depth of invasion (DOI) is part of the T stage and predicts occult neck metastases, so a tumour deeper than a few millimetres requires elective neck dissection even when the neck looks clean.
Why it matters in the exam
The commonest site is the lateral border of the tongue, then the floor of the mouth. Risk factors: smoking, alcohol, betel nut chewing, and premalignant lesions — erythroplakia (a red patch) carries a higher risk of malignant change than leukoplakia (a white patch). Any mouth ulcer that does not heal within 3 weeks requires biopsy. Under AJCC 8: T1 — up to 2 cm and DOI up to 5 mm; T2 — up to 2 cm with DOI over 5 to 10 mm, or 2 to 4 cm with DOI up to 10 mm; T3 — over 4 cm or DOI over 10 mm; T4a — invasion of the jaw bone or facial skin.
The D'Cruz study (2015) showed that elective neck dissection in early cancer with a clean neck improves survival compared with waiting. Under NCCN, dissection is considered when DOI is over 3 mm and almost always performed when DOI is over 4 mm; the usual type is selective dissection of levels I to III (supraomohyoid). Pathological margins of 5 mm or more are considered "clear". Sentinel node biopsy is an alternative in experienced centres.
The mandible: when the tumour touches bone without invading the marrow space — marginal mandibulectomy, which keeps bone continuity; with clear bone invasion — segmental resection and reconstruction with a free fibula flap. In an edentulous mandible the tumour enters through the ridge, so marginal resection is riskier. Adjuvant radiotherapy is given for pT3 to T4, multiple positive nodes, perineural or lymphovascular invasion; chemoradiotherapy with cisplatin is given for positive margins or extranodal extension (ENE), under the EORTC 22931 and RTOG 9501 trials.
Key points
- First treatment: surgery.
- DOI is part of the T stage.
- DOI over 3 to 4 mm — elective dissection.
- Bone invasion — segmental resection and fibula.
- Positive margins or ENE — chemoradiotherapy.
Summary table
| T stage | Size | Depth of invasion (DOI) |
|---|---|---|
| T1 | Up to 2 cm | Up to 5 mm |
| T2 | Up to 2 cm, or 2 to 4 cm | Over 5 to 10 mm, or up to 10 mm |
| T3 | Over 4 cm | Or over 10 mm |
| T4a | Invasion of jaw bone or skin | Any depth |
| Neck | DOI over 3 to 4 mm | Selective dissection I to III |
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Sources
- AJCC Cancer Staging Manual, 8th edition (2017) — Oral cavity
- NCCN Clinical Practice Guidelines in Oncology: Head and Neck Cancers — Cancer of the Oral Cavity, 2025 — Elective neck dissection and adjuvant therapy
- D'Cruz AK et al. Elective versus therapeutic neck dissection in node-negative oral cancer (NEJM), 2015 — Main results
Sources are given for further reading; the text is written afresh and not copied from them.
Reviewed by the Examqo AI Professor · 2026-11-06. The text may contain errors; when in doubt, check the source.