Postoperative Radiotherapy Improved Survival in pT1-2N1 Oral and Oropharyngeal Cancer Without Adequate Neck Dissection ​

Abstract Background: To assess the benefit of postoperative radiotherapy in patients with pT1-2N1M0 oral and oropharyngeal cancer by the quality of neck dissection.Methods: In the Surveillance, Epidemiology, and End Results database, pT1-2N1M0 oral and oropharyngeal cancer patients treated by primary tumor resection and neck dissection with or without radiotherapy were enrolled between 2004 and 2015. Univariate and multivariate analysis were used to explore the effect of adjuvant radiotherapy on 5-year overall survival (OS) and disease-specific survival(DSS).Results: Of the 1,765 patients identified, 1,108 (62.8%) had oral cancer, 1,141 (64.6%) were men, and 1,067 (60.5%) underwent adjuvant radiotherapy. After adjusting for confounding factors, postoperative radiotherapy reduced the adjusted hazard ratio (aHR) of 5-year OS to 0.64 (95% confidence interval[CI], 0.49-0.84) in those with <18 lymph nodes removed, but not in those with 19-24 lymph nodes removed (aHR, 0.78 ; 95% CI, 0.73-1.13), and in those with >25 lymph nodes removed (aHR, 0.96; 95% CI, 0.75-1.24). For 5-year DSS, similar effect was observed. The adjusted hazard ratio was 0.66 (95% confidence interval, 0.45-0.97) in those with <18 lymph nodes. The protective effect was not seen in those with 18-24 lymph nodes (aHR, 1.07; 95% CI 0.59-1.96), and in those with >25 lymph nodes (aHR, 1.12; 95% CI, 0.81-1.56). Sensitivity testing also showed a robust protective effect of postoperative radiotherapy in patients with <18 lymph nodes removed.Conclusion: Radiotherapy significantly improved survival in patients with pT1-2N1M0 oral and oropharyngeal cancer without adequate neck dissection.