Predictors of Distant Metastasis after Radical Surgery Followed by Postoperative Radiotherapy with or without Chemotherapy for Oropharyngeal Cancer

PURPOSE: We investigated the prognostic factors for distant metastasis (DM) in patients with locally advanced oropharyngeal cancer (OPC) treated with surgery and adjuvant radiotherapy with or without concurrent chemotherapy. MATERIALS AND METHODS: Eighty-five patients treated between January 1995 and August 2014 were evaluated retrospectively. Data regarding the pathological tumour and nodal status, human papillomavirus (HPV) status, treatment characteristics, and pretreatment maximum standardized uptake value (SUVmax) of 18-fluoro-2-deoxyglucose positron emission tomography–computed tomography scan ((18)F-FDG PET-CT) were evaluated, and their influence on DM and survival outcomes were analyzed. RESULTS: Median follow-up period was 48.0 months. Recurrence was observed in 20 patients, including locoregional recurrence and DM. DM was observed in 13 patients. A multivariate analysis confirmed that the presence of lymphovascular invasion (p=0.031), lower neck lymph node (LN) involvement (p=0.006), SUVmax ≥ 9.7 (p=0.014), and tumour size ≥ 3 cm (p=0.037) significantly affected DM. HPV status was not associated with DM. Perineural invasion (p=0.048), lower neck LNinvolvement (p=0.008), SUVmax ≥ 9.7 (p=0.019), and tumour size ≥ 3 cm (p=0.033) were also significant factors for the DM-free survival rate. CONCLUSION: Lower neck LN involvement, high SUVmax in pretreatment (18)F-FDG PET-CT, and large tumour size were predictive factors for DM in patients of OPC.