Lymph node ratio predicts the benefit of post-operative radiotherapy in oral cavity cancer

Background: The standard treatment for non-metastatic oral cavity squamous cell carcinoma (OCSCC) is surgical resection followed by post-operative radiotherapy (PORT) with/without chemotherapy in high risk patients. Given the substantial toxicity of PORT we assessed lymph node ratio (LNR) as a predictor of PORT benefit. Design: By using the Surveillance, Epidemiology and End Results (SEER) database, we analyzed all node positive OCSCC patients diagnosed between 1988 and 2007 who underwent neck dissection. LNR was categorized into three groups: <6%, 6-12.5% and >12.5%. Results: In 3091 subjects identified, median survival was 32, 25 and 16 months for LNR Groups 1, 2 and 3, respectively. On multivariate analysis, survival was associated with age, race, grade, tumor size, nodal stage, extra-capsular extension, use of PORT and LNR. When stratified by LNR group, PORT was associated with a survival benefit only in Group 3 (LNR > 12.5%): 2 year survival 25% vs 37%. No benefit to PORT was seen when the LNR ≤ 12.5%: 2 year survival 51% vs 54%. Conclusion: A low LNR is associated with extended survival in LN positive OCSCC. The survival benefit associated with PORT in this disease appears to be limited to those with a LNR > 12.5%. Validation is required prior to the clinical implementation of our findings.