Postoperative radiotherapy is associated with improved survival in pT1-2N1 oral and oropharyngeal cancer without adequate neck dissection

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 included 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) among different quality of neck dissection. RESULTS: Of the 1765 patients identified, 1108 (62.8%) had oral cancer, 1141 (64.6%) were men, and 1067 (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 (LNs) removed, but not in those with 19–24 LNs removed (aHR 0.78; 95% CI 0.73–1.13), and in those with ≥ 25 LNs 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 LNs. The protective effect was not seen in those with 18–24 LNs (aHR 1.07; 95% CI 0.59–1.96), and in those with ≥ 25 LNs (aHR 1.12; 95% CI 0.81–1.56). Sensitivity testing also showed a robust protective effect of postoperative radiotherapy in patients with < 18 LNs removed. CONCLUSION: Radiotherapy was associated with improved survival in pT1-2N1M0 oral and oropharyngeal cancer patients without adequate neck dissection.