Depth of Invasion (DOI) in Oral Cavity Cancers: AJCC 8th vs 9th Edition — What Changed?

Rodrigo Arrangoiz MS, MD, FACS, FSSO
  • Big Picture:
    • AJCC 8th Edition (2017):
      • Introduced Depth of Invasion (DOI) as a major determinant of T stage in oral cavity squamous cell carcinoma (OCSCC)
    • AJCC 9th Edition (2024 / 2025 update):
      • Retains DOI as a core component of T staging, with refinements and clarifications, not a paradigm shift
  • Key Concepts Introduced:
    • DOI ≠ tumor thickness
    • DOI measured from basement membrane of adjacent normal mucosa
    • DOI strongly correlates with:
      • Nodal metastasis
      • Survival
  • AJCC 9th Edition (What Changed?):
    • DOI Thresholds: UNCHANGED
      • The 5 mm and 10 mm cutoffs remain identical
      • DOI continues to upstage tumors independent of surface dimensions
      • This is critical:
        • No numeric change in DOI staging thresholds
    • Clarification of Measurement Technique:
      • The 9th edition places stronger emphasis on standardization and reproducibility:
        • Clearer distinction between:
          • Exophytic tumors (avoid overestimation)
          • Ulcerated lesions (reconstruct mucosal surface)
        • Addresses interobserver variability among pathologists
        • Reinforces:
          • Measurement from reconstructed basement membrane line
    • Integration With Other Risk Factors:
      • While DOI remains central, AJCC 9 emphasizes its interpretation within a broader biologic context:
        • DOI alone is not sufficient for prognosis
        • Must be integrated with:
          • Perineural invasion (PNI)
          • Lymphovascular invasion (LVI)
          • Worst pattern of invasion (WPOI) (not formally in AJCC but increasingly relevant)
          • Nodal disease / ENE
  • This reflects modern understanding:
    • Tumor biology > single metric
  • Clinical vs Pathologic DOI:
    • Reinforces distinction:
      • cDOI (imaging / clinical) vs pDOI (pathologic gold standard)
    • Encourages better use of:
      • MRI / ultrasound for preoperative planning
  • What Did NOT Change
    • DOI is still:
      • A T-category modifier, not a standalone staging variable
      • Only used in oral cavity cancers (not oropharynx, etc)
      • No change to:
        • T1 / T2 / T3 definitions based on DOI
        • Surgical decision-making thresholds (though clinical use continues evolving)
  • Practical Clinical Impact (2025 Reality):
    • Surgical Oncology Perspective:
      • DOI continues to guide:
        • Elective neck dissection:
          • DOI ≥ 3 mm to 4 mm → strong consideration
        • Margin planning
        • Adjuvant therapy discussions
    • Research / Modern Trends:
      • DOI is increasingly being:
        • Combined with molecular markers
        • Supplemented by AI-based histologic risk models
        • Some argue DOI may eventually be:
          • Refined or replaced by composite risk scores
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Published by Rodrigo Arrangoiz MS, MD, FACS, FSSO

My name is Rodrigo Arrangoiz I am a breast surgeon/ thyroid surgeon / parathyroid surgeon / head and neck surgeon / surgical oncologist that works at Center for Advanced Surgical Oncology in Miami, Florida. I was trained as a surgeon at Michigan State University from (2005 to 2010) where I was a chief resident in 2010. My surgical oncology and head and neck training was performed at the Fox Chase Cancer Center in Philadelphia from 2010 to 2012. At the same time I underwent a masters in science (Clinical research for health professionals) at the University of Drexel. Through the International Federation of Head and Neck Societies / Memorial Sloan Kettering Cancer Center I performed a two year head and neck surgery and oncology / endocrine fellowship that ended in 2016. Mi nombre es Rodrigo Arrangoiz, soy cirujano oncólogo / cirujano de tumores de cabeza y cuello / cirujano endocrino que trabaja Center for Advanced Surgical Oncology en Miami, Florida. Fui entrenado como cirujano en Michigan State University (2005 a 2010 ) donde fui jefe de residentes en 2010. Mi formación en oncología quirúrgica y e n tumores de cabeza y cuello se realizó en el Fox Chase Cancer Center en Filadelfia de 2010 a 2012. Al mismo tiempo, me sometí a una maestría en ciencias (investigación clínica para profesionales de la salud) en la Universidad de Drexel. A través de la Federación Internacional de Sociedades de Cabeza y Cuello / Memorial Sloan Kettering Cancer Center realicé una sub especialidad en cirugía de cabeza y cuello / cirugia endocrina de dos años que terminó en 2016.

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