Treatment response in the neck: p16+ versus p16− oropharyngeal cancer

INTRODUCTION: To compare nodal response rates following chemoradiotherapy in patients with p16+ and p16- oropharyngeal squamous cell carcinoma (OPSCC). METHODS: Patients with node-positive OPSCC treated at Peter MacCallum Cancer Centre on the published phase I-III tirapazamine trials were identified. All patients had conventional assessment (clinical examination (CA), CT and/or MRI) and positron emission tomography (PET) at both baseline and 2-4 months post-treatment. RESULTS: There were 30 p16+ and 18 p16- patients, the former group having significantly higher stage nodal disease (P = 0.016). The mean overall reduction in nodal size at post-treatment assessment was similar in p16+ and p16- patients (78% vs. 75%), and no statistically significant difference in nodal complete response (CR) rates was detected by either CA (50% vs. 39%, P = 0.35) or PET/PET-CT (93% vs. 83%, P = 0.19). PET was significantly more accurate in determining the true nodal CR rate in both groups, with a negative predictive value of 96%. CONCLUSION: Nodal response rates following chemoradiotherapy appear to be similar in p16+ and p16- patients when assessed by either CA or PET/PET-CT. However, higher nodal CR was seen in PET/PET-CT compared with CA in both groups. Metabolic imaging is more accurate than CA in assessing nodal response post-treatment.