18 FDG PET/CT prediction of treatment outcomes in patients with p16-positive, non-smoking associated, locoregionally advanced oropharyngeal cancer (LA-OPC) receiving deintensified therapy: Results from NRG-HN002.

Abstract

6563 Background: To determine the negative predictive value (NPV) of 12-14 week post-treatment PET/CT for 2-year progression-free survival (PFS) and 2-year locoregional control (LRC) in NRG-HN002, which is a two-arm phase II trial for patients with low-risk, non-smoking associated p16-positive LA-OPC randomized in a 1:1 ratio to reduced-dose IMRT with or without cisplatin. Methods: PET/CT scans were reviewed both centrally and locally by participating institutions. Tumor response evaluations for primary site, right neck, and left neck were carried out using a 5-point ordinal scale (‘Hopkins Criteria’). Overall scores were then assigned as ‘Negative,’ Positive,’ or ‘Indeterminate.’ Patients who had a ‘Negative’ score for all three evaluation sites were given an overall score of ‘Negative.’ The endpoints were NPV for LRC and PFS at 2 years testing NPV ≤ 90% vs > 90% (1-sided alpha 0.10 and 76% power). Results: There were 316 patients enrolled, of whom 306 were randomized and eligible. Of these, 131 (42.8%) patients consented to a post-therapy PET/CT, and 117 (89.3%) patients were eligible for PET/CT analysis. The median time from end of treatment to PET/CT scan was 94 days (range 52-139). The rates of 2-yr PFS and LRC in the analysis subgroup were 91.3% and 93.8%, respectively. Based on central review, post-treatment scans were negative for residual tumor for 115 patients (98.3%) and positive for 2 patients (1.7%). The NPV for 2-year LRC was 94.5% (90% lower confidence bound [LCB] 90.6%; p = 0.07). NPV for 2-year PFS was 92.0% (90% LCB 87.7%; p = 0.30). Similar NPV results were obtained based on analysis of local reviews. Conclusion: Within the context of deintensification with reduced-dose radiation, the NPV of a 12-14 week post-therapy PET/CT for 2-year LRC is statistically > 90%, similar to that reported for patients receiving standard chemoradiation. However, in this study, there was not enough evidence to conclude that the NPV of a 12-14 week post-therapy PET/CT for 2-year PFS is > 90%. Grant acknowledgement: This project was supported by grants U10CA180868 (NRG Oncology Operations), U10CA180822 (NRG Oncology SDMC), U24CA180803 (IROC), UG1CA189867 (NRG Oncology NCORP) from the National Cancer Institute (NCI). This project is funded, in part, under a Grant with the Pennsylvania Department of Health. The Department specifically disclaims responsibility for any analyses, interpretations or conclusions. Clinical trial information: NCT02254278 .