Prognostic Value of p16 Status on the Development of a Complete Response in Involved Oropharynx Cancer Neck Nodes After Cisplatin-Based Chemoradiation: A Secondary Analysis of NRG Oncology RTOG 0129

Purpose To determine the relationship between p16 status and the regional response of patients with node-positive oropharynx cancer treated on NRG Oncology RTOG 0129. Methods and Materials Patients with N1-N3 oropharynx cancer and known p16 status who underwent treatment on RTOG 0129 were analyzed. Pathologic complete response (pCR) rates in patients treated with a postchemoradiation neck dissection (with p16-positive or p16-negative cancer) were compared by Fisher exact test. Patients managed expectantly were compared with those treated with a neck dissection. Results Ninety-nine (34%) of 292 patients with node-positive oropharynx cancer and known p16 status underwent a posttreatment neck dissection (p16-positive: n=69; p16-negative: n=30). The remaining 193 patients with malignant lymphadenopathy at diagnosis were observed. Neck dissection was performed a median of 70 (range, 17-169) days after completion of chemoradiation. Neither the pretreatment nodal stage ( P =.71) nor the postradiation, pre-neck dissection clinical/radiographic neck assessment ( P =.42) differed by p16 status. A pCR was more common among p16-positive patients (78%) than p16-negative patients (53%, P =.02) and was associated with a reduced incidence of local–regional failure (hazard ratio 0.33, P =.003). On multivariate analysis of local–regional failure, a test for interaction between pCR and p16 status was not significant ( P =.37). One-hundred ninety-three (66%) of 292 of initially node-positive patients were managed without a posttreatment neck dissection. Development of a clinical (cCR) was not significantly influenced by p16-status ( P =.42). Observed patients with a clinical nodal CR had disease control outcomes similar to those in patients with a pCR neck dissection. Conclusions Patients with p16-positive tumors had significantly higher pCR and locoregional control rates than those with p16-negative tumors.