Tumor thickness influences prognosis of T1 and T2 oral cavity cancer--but what thickness?

BACKGROUND

Previous studies have demonstrated that tumor thickness might influence prognosis in oral cancer, but the significant point at which outcome changes has varied from 1.5 mm to 6 mm. The clinical relevance of thickness remains unclear, and a reproducible prognostic "breakpoint" needs to be defined.

METHODS

Tumor thickness was measured in 145 oral cavity squamous cancers, clinically staged T1 (n = 62) or T2 (n = 83). Clinical and pathologic data were collected prospectively between 1988 and 2000, but thickness was measured on paraffin sections for this study. Minimum follow-up was 2 years, and thickness was correlated with local control, cervical node involvement, and survival. Patients with clinically positive nodes (n = 21) were not excluded. Overall, 55 patients had pathologic node involvement at some time in their disease.

RESULTS

Median tumor thickness was 6.2 mm, and there was little variation between sites: tongue, 6.4 mm; floor of mouth, 6.6 mm; and other sites, 5.7 mm. Median thickness for T1 tumors was 4.3 mm, significantly less than the T2 group, 8 mm (p <.01). Median thickness also varied significantly for tumors with associated nodal disease (8.5 mm) and without nodal disease (5.8 mm) (p <.01). Prognosis changed significantly at a cutoff of 4 mm with local control, nodal disease, and survival rates of 91%, 8%, and 100%, respectively, for tumors <4 mm compared with 84%, 48%, and 74% for those 4 mm or more thick (p <.01). Subgrouping greater than and less than 3 mm and 5 mm also showed a difference but with poorer discrimination. Thickness and pathologic nodal involvement were highly significant independent prognostic factors.

CONCLUSIONS

Tumor thickness is a highly significant, objectively measurable prognostic factor in early stage oral cancers. There is a need to standardize techniques of measurement to allow a multi-institutional study to be carried out. This will facilitate the development of strategies aimed at improving the outcome of higher risk patients.