title: Tumor classification for early oral cancer: re-evaluate the current TNM classification.
abstract: BACKGROUND
  We hypothesized that incorporation of tumor thickness into the tumor-node-metastasis (TNM) system will provide better prognostic information. Tumors were reclassified as T1 if ≤5-mm thick/≤4-cm diameter, and T2 if >5-mm thick/≤4-cm diameter.
  
  
  METHODS
  A retrospective analysis was conducted of 322 patients with T1 and T2 oral squamous cell carcinoma (SCC) between 1987 and 2012. Univariable survival analysis was performed using the log-rank test and multivariable analysis using the Cox proportional hazards model.
  
  
  RESULTS
  Multivariable analysis confirmed that tumor thickness is the most important predictor of disease-specific survival (DSS; hazard ratio [HR], 2.7; p = .03) and overall survival (OS; HR, 2.9; p = .001). Using the current TNM classification system, there is no significant difference in survival between the T1 and T2 groups for DSS (p = .13) or OS (p = .66). The revised staging system was superior at stratifying patients according to the T classification for both DSS (p = .016) and OS (p < .001).
  
  
  CONCLUSIONS
  Tumor thickness is an important prognostic indicator in early oral SCC and should be incorporated in the TNM classification system.
authors.affiliation: Sydney Head and Neck Cancer Institute, Royal Prince Alfred Hospital and University of Sydney, New South Wales, Australia; Department of Otolaryngology, Royal Prince Alfred Hospital, New South Wales, Australia.
authors.forename: Tsu-Hui
authors.initials: TH
authors.lastname: Hubert Low
authors.forename: Kan
authors.initials: K
authors.lastname: Gao
authors.forename: Michael
authors.initials: M
authors.lastname: Elliott
authors.forename: Jonathan R
authors.initials: JR
authors.lastname: Clark
mesh_terms: D002294:Carcinoma, Squamous Cell / Q000401:mortality / Q000473:pathology* / Q000628:therapy; D018572:Disease-Free Survival; D006801:Humans; D008875:Middle Aged; D009062:Mouth Neoplasms / Q000401:mortality / Q000473:pathology* / Q000628:therapy; D009361:Neoplasm Invasiveness; D009367:Neoplasm Staging; D011379:Prognosis; D012189:Retrospective Studies
keywords: depth of invasion; head and neck cancer; oral cavity/mouth neoplasm; staging; tumor thickness