Tumor thickness versus depth of invasion: analysis of the 8th edition American Joint Committee on Cancer Staging for oral cancer

Objectives: The primary aim of this study is to compare the effect of using tumor thickness versus depth of invasion (DOI) to determine the 8th edition AJCC T-category on survival in a large cohort of OSCC. Materials and methods: A retrospective cohort study of patients whose clinicopathologic information had been collected prospectively into a dedicated head and neck database. 927 patients with oral SCC were identified in this cohort, with the final study population including 456 patients with complete information on DOI, tumor thickness, T and N staging and follow-up. Results: 26 (5.7%) patients had a different AJCC 8 T category when using thickness instead of depth. 15 were upstaged from T1 to T2, 10 upstaged from T2 to T3 and 1 down staged from T2 to T1. Additionally, similar stratification of disease-specific and overall survival curves were found for T category based on DOI and thickness. Conclusion: The T category and TNM stage prognostic performance of 8th edition AJCC staging of oral cancer is similar regardless of whether DOI or thickness is used as the T-category modifier. In centers without complete DOI data it is reasonable to impute thickness for retrospective survival analyses using the 8th edition of the AJCC staging system.