Depth of invasion for prognostic stratification in oral cavity cancer: do we need further validation?

The tumor-node-metastasis (TNM) staging system of the American Joint Cancer Committee (AJCC)/Union for International Cancer Control (UICC) is a tool originally conceived for description of disease extent, aimed at providing prognostic information and making useful “post hoc” comparisons possible between different centers/series and/or therapeutic strategies. Nevertheless, in everyday clinical practice, it is frequently (and inappropriately) employed “upfront” in choosing primary and/or complementary treatment(s) for a given patient. To correctly assign outcomes categories and possibly (de-) escalate treatment accordingly, a staging system should identify distinct prognostic stratifications that must be internally homogeneous, while at the same time differing from one another. Moreover, when aiming towards more finely-tuned staging accuracy, TNM should remain relatively simple, user friendly, and reproducible.