The 8th TNM classification for oral squamous cell carcinoma: What is gained, what is lost, and what is missing

Abstract

Objectives: The 8th TNM edition remarkably changed the classification of T and N categories for oral squamous cell carcinoma (OSCC). The present study aims at evaluating the improvement in prognostic power compared to the 7th edition, pros and cons of the modifications, and parameters deserving consideration for further implementations.

Materials and methods: All OSCCs treated with upfront surgery at our institution between 2002 and 2017 were included. Demographics, clinical-pathological and treatment variables were retrieved. All tumors were classified according to both the 7th and 8th TNM edition, and patients were grouped according to the shift in T category and stage. Survivals were calculated with the Kaplan-Meier method. Univariate and multivariate analysis were carried out. Receiver Operating Characteristics (ROC) curve analyses were performed to find the best cut-off of DOI (in patients with DOI > 10 mm) and number of involved nodes (in positive neck patients).

Results: 244 patients were included. T, N categories, and stage changed in 59.2%, 20.5%, and 49.1% patients, respectively; 41.5% of patients were upstaged. The new T classification well depicted prognosis according to OS. Five-year overall (OS), disease-specific, recurrence-free (RFS) survivals were 60.5%, 70.9%, 59.8%, respectively. According to ROC curves, DOI > 20 mm and 4 positive nodes were the best cutoffs for OS and RFS.

Conclusion: The novelties introduced in 8th TNM edition were positive. DOI > 20 mm for T4 definition and number of positive nodes (0, <4, 4 or more) for N classification emerged as the most urgent factors to be implemented.

Keywords: 8th TNM edition; Depth of invasion; Nodal metastasis; Number of positive nodes; Oral cancer; Oral squamous cell carcinoma; Perineural invasion.