Squamous cell carcinoma of unknown primary of the head and neck: Favorable prognostic factors comparable to those in oropharyngeal cancer.

Abstract

Treatment for squamous cell carcinoma (SCC) of unknown primary consists of radiotherapy (RT) +/- chemotherapy or neck dissection +/- adjuvant RT/chemoradiotherapy (CRT). We compared these strategies and identified prognostic factors. From 1993 to 2015, 75 patients with SCC of unknown primary had RT-based or surgery-based treatment. Primary endpoints were overall survival (OS) and disease-free survival (DFS). Event-time distributions were estimated using the Kaplan-Meier method. Five-year OS and DFS for RT-based and surgery-based treatments were similar (OS 73% vs 68%, respectively; DFS 65% vs 64%, respectively). Among 38 patients with p16 data, 76% were p16 positive and showed improved 5-year DFS (90% vs 33%; P = .001) and OS (96% vs 33%; P < .001). Smoking history ≤10 pack-years conferred better 5-year DFS (88% vs 49%; P < .001) and OS (91% vs 59%; P < .001). RT-based and surgery-based treatments produced similar outcomes. Patients with p16-positive disease with ≤10 pack-years of smoking history and limited nodal stage constitute a "low-risk" group in SCC of unknown primary similar to that in oropharyngeal cancer.