Depth of invasion alone as an indication for postoperative radiotherapy in small oral squamous cell carcinomas: An International Collaborative Study

Head Neck. 2019 Jun;41(6):1935-1942. doi: 10.1002/hed.25633. Epub 2019 Feb 24.


Background: We aimed to investigate whether depth of invasion (DOI) should be an independent indication for postoperative radiotherapy (PORT) in small oral squamous cell carcinomas (SCC).

Methods: Retrospective analysis of DOI (<5, 5 to <10, ≥10 mm) and disease-specific survival (DSS) in a multi-institutional international cohort of 1409 patients with oral SCC ≤4 cm in size treated between 1990-2011.

Results: In patients without other adverse factors (nodal metastases; close [<5 mm] or involved margins), there was no association between DOI and DSS, with an excellent prognosis irrespective of depth. In the absence of PORT, the 5-year disease-specific mortality was 10% with DOI ≥10 mm, 8% with DOI 5-10 mm, and 6% with DOI <5 mm (P = .169), yielding an absolute risk difference of only 4%.

Conclusion: The deterioration in prognosis with increasing DOI largely reflects an association with other adverse features. In the absence of these, depth alone should not be an indication for PORT outside a clinical trial.

Keywords: depth of invasion; head and neck cancer; locoregional control; oral squamous cell carcinoma; radiotherapy; survival; tumor thickness.

Publication types

  • Multicenter Study

MeSH terms

  • Adult
  • Aged
  • Carcinoma, Squamous Cell / pathology*
  • Carcinoma, Squamous Cell / radiotherapy*
  • Carcinoma, Squamous Cell / surgery
  • Female
  • Humans
  • Male
  • Margins of Excision
  • Middle Aged
  • Mouth Neoplasms / pathology*
  • Mouth Neoplasms / radiotherapy*
  • Mouth Neoplasms / surgery
  • Neoplasm Invasiveness
  • Patient Selection
  • Radiotherapy, Adjuvant
  • Retrospective Studies
  • Risk Factors