Lymph node ratio as a prognostic marker of oral tongue squamous cell carcinoma: a cohort study

INTRODUCTION Lymph node metastasis is a poor prognostic indicator and is well established in tongue squamous cell carcinoma. Based on the current staging system, accurate risk stratification is difficult. There is thus a need to evaluate an alternate method for predicting recurrence and survival. The objective of the study was to evaluate lymph node ratio as a prognostic marker as compared with N-staging for tongue squamous cell carcinoma. MATERIALS AND METHODS We conducted a retrospective cohort study with 56 patients with a lymph node ratio greater than 0.012 (exposed) and 74 patients with a lymph node ratio less than 0.012 (unexposed). Overall five-year survival and disease-free survival were assessed. The Cox proportional hazard model was used to analyse lymph node ratio as a predictor of outcome, together with other covariates. RESULTS A total of 130 patients were included in the study. Patients with lymph node ratio greater than 0.012 had a poor overall five-year (mean survival time 52.1 months vs 38.1 months) and disease-free survival (mean survival time 53.6 months vs 39.2 months). The hazard of death among patients with a lymph node ratio greater than 0.012 was 3.24 times higher than the hazard of death among patients with a lymph node ratio less than 0.012 (95% confidence interval 1.82-5.77). DISCUSSION Lymph node ratio is a superior prognostic marker compared with the currently used American Joint Committee on Cancer N-staging. Our findings also suggest that the margin status (involved) of the primary tumour resection adversely affects prognosis.