Tumor classification for early oral cancer: re-evaluate the current TNM classification.

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). CONCLUSION: Tumor thickness is an important prognostic indicator in early oral SCC and should be incorporated in the TNM classification system.