Circulating tumor HPV DNA reappearance as an early indicator of recurrence after radiotherapy-based treatment for HPV-associated oropharyngeal cancer: analysis of more than 2000 assessments in 232 patients.

BACKGROUND: Circulating tumor human papillomavirus DNA (ctHPV DNA) is a promising blood-based surveillance biomarker in HPV-positive oropharyngeal squamous cell carcinoma (OPSCC) and head-and-neck carcinoma of unknown primary (CUP). This study aimed to evaluate the diagnostic performance of ctHPV DNA-based molecular testing for detecting disease recurrence. METHODS: Patients with OPSCC/CUP treated at our institution between 2012 and 2024 who had detectable ctHPV DNA in plasma at baseline were included. All patients underwent prospective serial ctHPV DNA surveillance using quantitative PCR. RESULTS: 2928 assessments were performed in 232 patients, including 2192 surveillance tests. Among 220 patients who achieved complete radiologic and molecular response, ctHPV DNA reappearance showed 90.3% sensitivity, 97.9% specificity (Sp), 87.5% positive predictive value (PPV), and 98.4% negative predictive value (NPV) for detecting clinically confirmed recurrence. CtHPV DNA reappearance preceded clinical recurrence in 58.1% of recurrent cases. In per-test interval-based analyses, sensitivity peaked at 90.9% at 45 days, while specificity and NPV remained high (Sp 97.6%-98.8%, NPV ≥ 98.9%) across all time intervals (14-180 days). CtHPV DNA positivity at 1 month after radiotherapy-based treatment completion was strongly associated with worse overall survival (HR 19.1, 95% CI 7.5-48.8) and disease-free survival (HR 15.4, 95% CI 6.7-35.4), whereas the result obtained immediately after treatment had limited prognostic value. CONCLUSIONS: Longitudinal qPCR-based ctHPV DNA monitoring may complement standard post-treatment surveillance in baseline ctHPV DNA-positive HPV-associated OPSCC/CUP by identifying patients at very low short-term risk of recurrence and by providing an early signal of molecular recurrence before clinical confirmation in a subset of patients.