Patients with low lying lymph nodes are at high risk for distant metastasis in oropharyngeal cancer

Purpose We sought to identify risk factors for distant metastasis (DM) in patients with oropharyngeal cancer (OPC) and perform a recursive partition analysis (RPA) to identify patients both at low and high risk for DM. Methods Our center treated 647 consecutive OPC patients with IMRT between 9/98 and 1/12. The following clinical features were used as prognostic factors: T Stage, N Stage, smoking history, tumor grade, tumor sub-site, the presence of a low lying (level IV or VB) lymph node (LLLN). A Cox model of the risk of DM was used to identify independent prognostic factors. RPA was used to identify patients at low, intermediate, and high risk for DM. Results The median follow-up time in living patients was 42.2 months (range: 2-166). The primary OPC site was the tonsil in 296 patients, base of tongue in 315 patients, and soft palate or pharyngeal wall in 36 patients. For the entire cohort, the Kaplan-Meier estimate for 3 year freedom from distant metastasis was 88.4%. A Cox model identified T Stage (p < 0.001), N Stage (p = 0.02), and LLLN (p = 0.002) as independent predictors of DM. RPA identified patients at low, intermediate, and high risk of DM, with a 3-year freedom-from DM of 98%, 91.1%, and 65.4% respectively. Conclusion The presence of a low lying lymph node is significantly associated with an increased risk of DM in OPC. RPA identified patients both at very low and very high risk for DM with information routinely obtained in clinic.