Proposal for modification of the TNM staging classification for cancer of the oral cavity. DOSAK

Abstract

Aim: The prognostic value of the TNM and pTNM classifications currently used for tumours of the oral cavity is unsatisfactory. A better classification should be aimed at as today's definition of T4 leads to overclassification of many tumours and today's definition of N3 results in too few lymph nodes in this group. Until 1987 the grade of fixation of lymph-nodes was part of the N-classification for oral cancer as it is currently used in the N-classification of breast cancer.

Methods: From 1987 to 1991 the DOSAK tumour registry has stored 1532 primary cases of cancer of the oral cavity from 23 hospitals. Crosstables were applied to outline the classification rule for clinical and histopathological T and N based on important factors (T: tumour diameter and thickness; N: lymph node diameter and grade of fixation; pT: histopathological tumour diameter and thickness; pN: number of lymph nodes involved by the tumour). A Cox model was calculated and combinations of similar prognostic estimates were summarized to the same clinical and histopathological T and N. It was aimed at separating categories and achieving equivalent clinical and histopathological T classifications and group frequencies. In a final step a clinical and histopathological stage grouping can be proposed.

Results: The gradation of the survival rates shows a marked separation between the T, N and stage categories. The distribution of T, N and stage categories was more uniform when applying the new classification.