Kinetics of Circulating Human Papillomavirus (cHPV) DNA in Plasma and Oral Gargles From Patients with HPV-Positive Oropharyngeal Cancer (OPC) Treated with Definitive Radiation Therapy

Abstract

<h3>Purpose/Objective(s)</h3> Changes in cHPV DNA copy numbers and absence of detectable oral HPV DNA during and after treatment may be biomarkers of treatment response and recurrence. The goal of this study was to assess the kinetics of oral and plasma HPV DNA among HPV positive OPC patients pre, during and post radiation treatment. <h3>Materials/Methods</h3> Patients with T0-2 N0-1 p16 positive OPC were enrolled to a personalized radiation treatment trial where a total dose of 60-70 Gy based on size of largest lesion was delivered. Plasma and oral gargle was collected prior to treatment, during week 4 of treatment, at end of treatment (EOT), and 2-3 months post-treatment. Tumor-tissue-modified human papillomavirus (TTMV) DNA copy numbers were quantified in plasma (Naveris, Natick, MA). HPV genotyping of oral cell DNA was performed utilizing the HPV SPF₁₀ PCR-DEIA-LiPA₂₅ line probe assay system. Statistics were performed via Fisher's exact test. <h3>Results</h3> 33 patients with circulating TTMV and oral HPV genotyping were included. Patients with tonsil primaries were more likely to have detectable oral HPV (9/13) compared with BOT (6/20) (p=0.038). Of the 30 patients that were plasma TTMV positive, 15 were oral gargle positive. Of the 30 pretreatment TTMV positive patients, 11 of 30 (36.7%) had undetectable TTMV levels at week 4 of radiation therapy, 18 of 29 patients (62.1%) were TTMV negative by EOT, and 26 of 27 (96.3%) patients were negative at 3 months post-treatment. The one patient who remained TTMV positive at 3 months had a bone metastasis. Retrospective review of pretreatment imaging revealed that this was an undiagnosed metastasis in the bone at the time of trial enrollment. Oral HPV DNA was cleared in 12 of the 15 initially positive patients (80%) at 4 weeks, 14 of 15 patients (93.3%) at EOT, and 15 of 15 patient (100%) at 3 months. All patients had no evidence of disease clinically and radiologically at their 3 month post-treatment follow up visit, except for the one patient who was metastatic at presentation. TTMV clearance at 4 weeks was associated with a >30% volumetric imaging response at 4 weeks with 13 of 14 patients who had undetectable TTMV levels at 4 weeks also having with a >30% volumetric response as compared to 5 of 13 patients who did not have TTMV HPV clearance at 4 weeks but having a >30% volumetric imaging response (p=0.003). Clearance of oral HPV DNA was not associated with a partial response at 4 weeks. <h3>Conclusion</h3> Circulating TTMV copy numbers are detected in the majority of p16 positive OPC at diagnosis. TTMV clearance at 4 weeks is associated with a robust radiological response, suggesting radiosensitivity. These patients may represent a subset that would be candidates for de-escalation strategies.