Validation of the 8th edition of the AJCC/UICC TNM staging system for tongue squamous cell carcinoma

Background The revised 8th edition of the AJCC/UICC staging system was released in January 2017, and depth of invasion (DOI) was added to the new criteria for T classification in oral cavity cancer. In this study, we evaluated whether the 8th edition presents the prognosis and risk of nodal metastasis in patients with squamous cell carcinoma of tongue more accurately than did the 7th edition. Methods The data for 112 patients were obtained and reclassified based on the criteria presented in the 8th edition. Results Seven patients previously staged as T1 based on the criteria in the 7th edition were reclassified as T2 based on the 8th edition, while 19 T2 patients were reclassified as T3, and 9 T4a patients were reclassified as T3. T3 in the 8th edition represents a homogenous population showing the same prognosis, while T2 in the 8th edition represents a heterogenous population. Nodal metastasis was significantly correlated with T classification in both editions and DOI. However, neither the T classification in the 7th or 8th edition, nor DOI could predict the probability of potential nodal metastasis in patients with cN0 disease. Conclusions The classification on T3 in the 8th edition can be seen as reasonable with regard to prognosis. Nodal metastasis was significantly correlated with T classification and DOI; however, the probability of subsequent nodal metastasis in patients with T2N0 was almost same for the criteria in the 7th and 8th editions, therefore, the same careful management as before is required for patients with N0 disease.