ENT Liu Knowledge Base Head & neck tumours · physician reviewed
Oral Cavity Cancer · Symptoms & diagnosis

What is depth of invasion and why does it change the operation?

Reviewed: 8 November 2026 By: Xiangpeng Liu, MD Topic: Oral Cavity Cancer Answer length: short, citable
Quick answer

Depth of invasion (DOI) measures how far the tumour has grown downward from the surface, in millimetres. In AJCC 8th edition it upstages the T category, because thicker tongue and floor-of-mouth cancers have a much higher rate of microscopic neck-node spread even when the neck feels normal on examination.

In detail

For this reason, a clinically node-negative oral cancer with a DOI beyond roughly 3–4 mm is commonly treated with an elective neck dissection or a sentinel lymph node biopsy at the same operation as the primary excision. Ask your surgeon for the DOI value in the pathology report.

What this means in practice: this answer is part of the “Symptoms & diagnosis” section of the Oral Cavity Cancer topic. If you are comparing treatment options, also read how to compare a second opinion and which records to send.

Other common questions about oral cavity cancer

See all 15 questions in this topic →

Sources for this answer

  1. NCCN Guidelines for Patients: Head and Neck Cancers National Comprehensive Cancer Network · 2025
  2. Head and Neck Cancers (patient information) US National Cancer Institute · 2025

Written and medically reviewed by Xiangpeng Liu, MD

Associate Chief Physician, ENT & Head/Neck Surgery · Chenzhou First People’s Hospital, Chenzhou, Hunan, China

Editorial policy & reviewer credentials · All sources

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Medical disclaimer: This knowledge base is general information for people researching head and neck tumours, not a diagnosis or treatment plan. It does not replace an examination by a qualified physician. Survival figures are population averages, not predictions for an individual. Treatment and cost estimates for China are illustrative only and must be confirmed in writing after your records have been reviewed. If you have a symptom lasting more than two to three weeks, see a doctor promptly.