Significance of Negative Posttreatment 18-FDG PET/CT Imaging in Patients With p16/HPV-Positive Oropharyngeal Cancer

Purpose: Patients with p16/human papilloma virus (HPV)-associated oropharyngeal squamous cell carcinoma have a favorable outcome after treatment. In this group of patients who could have a long life expectancy, the optimal surveillance strategy and modality is not well established. We aim to determine the ability of a negative postradiation positron emission tomography (PET)/computed tomography scan to predict the risk of subsequent relapse in these patients.

Materials and methods: A retrospective analysis of patients with p16/HPV-associated oropharyngeal squamous cell carcinoma who completed definitive (chemo)radiation therapy and had a posttreatment PET/computed tomography scan from 2006 to 2013 was performed. Patient, tumor, and treatment characteristics and clinical outcomes were recorded. Tumors were considered HPV/p16 positive if either HPV (by in situ hybridization) or p16 (by immunohistochemistry) was positive. Disease-free survival and overall survival rates were estimated using the Kaplan-Meier method.

Results: In our study, 327 patients were evaluated. The median age was 57 years. The most common primary sites were base of tongue (50%) and tonsil (48%). Of the patients evaluated, 291 (89%) had a negative posttreatment PET scan. For these 291 patients who had a complete metabolic response after treatment, the 5-year disease-free survival and overall survival rates were 91% and 89%, respectively. The median time to development of recurrence was 16 months. Of the 291 patients, 24 patients (8%) had disease recurrence; 13 recurrences were locoregional, and 13 were distant. Eleven (4%) patients with recurrence had further surgery or radiation, and 8 patients (3%) were without disease as of the last follow-up.

Conclusions: Patients who achieve a complete metabolic response on posttreatment PET imaging have an excellent prognosis, and the risk of developing a recurrence in the future is very low. Therefore, a more cost effective surveillance program should be considered for this subgroup of patients.