Abstract Background: Cell-free HPV-DNA (cfHPV-DNA) in plasma represents a promising biomarker to grade treatment response and monitor for persistence/recurrence. We evaluated the dynamic changes of cfHPV-DNA during induction chemotherapy followed by response-stratified de-escalation in HPV associated (HPV+) oropharyngeal squamous cell cancer (OPSCC). Methods: A prospective biomarker clinical trial of response-stratified de-escalation therapy was conducted. Eligible patients had loco-regional HPV+ OPSCC and received induction chemotherapy with carboplatin and paclitaxel for three cycles followed by risk and response-stratified de-escalation with transoral robotic surgery (TORS), de-escalated radiation (RT) to 50Gy with or without cisplatin, or standard RT to 70Gy with cisplatin. Patients with deep response (&amp;gt;=50% tumor shrinkage per RECIST 1.1) qualified for de-escalated therapy. Cell-free HPV-DNA was measured using a CLIA-certified HPV-SEQ assay that utilizes NGS technology to detect and quantify HPV16 and HPV18 DNA in plasma at baseline, after each cycle of induction chemotherapy, during radiation, and post-treatment surveillance at 3, 6, 9, 12, 18, and 24 months following treatment. Results: Forty-six eligible patients were enrolled, with 464 cfHPV-DNA plasma samples analyzed (median 10 samples per patient). There were five recurrences (10.9%), all detected by HPV-SEQ. Baseline cfHPV-DNA was detected in 44/46 patients (96%). Patients with rapid early cfHPV-DNA clearance after one 3-week cycle of induction (&amp;gt;=95% clearance) predicted deep radiographic response following induction therapy (p=0.003). The detection of cfHPV-DNA at 3 months or later after treatment was associated with worse progression free survival (PFS), with 2-year PFS of 25% (95% CI 0.012-0.65) compared with patients without detectable cfHPV-DNA of 100% (95% CI 1.0-1.0); p&amp;lt;0.001). The longest lead-time from positive cfHPV-DNA to developing recurrent disease was 25 months. Conclusion: Rapid early clearance of cfHPV-DNA during induction has utility in predicting response to treatment. Detectable cfHPV-DNA following treatment is strongly associated with worse PFS. A subsequent trial using cfHPV-DNA to select patients for treatment de-escalation is ongoing. Clinicaltrials.gov ID: NCT04572100 Citation Format: Ari Rosenberg, Evgeny Izumchenko, John Cursio, Augustin Vannier, Aditya Juloori, Rohan Katipally, Rifat Hasina, Frederick Jones, Anna Starus, Elizabeth Blair, Daniel J. Haraf, Alexander T. Pearson, Everett E. Vokes, Nishant Agrawal. Cell-free HPV-DNA dynamics during induction chemotherapy and response-stratified de-escalation in viral-mediated oropharyngeal cancer [abstract]. In: Proceedings of the AACR Special Conference: Liquid Biopsy: From Discovery to Clinical Implementation; 2024 Nov 13-16; San Diego, CA. Philadelphia (PA): AACR; Clin Cancer Res 2024;30(21_Suppl):Abstract nr B023.

Abstract B023: Cell-free HPV-DNA dynamics during induction chemotherapy and response-stratified de-escalation in viral-mediated oropharyngeal cancer