Integrating Pretreatment Circulating Tumor HPV DNA and Tumor Volume for Risk Stratification in HPV-Positive...

Circulating tumor HPV DNA (ctHPV DNA) has shown clinical value in HPV-positive oropharyngeal squamous cell carcinoma (OPSCC), but its relationship with tumor burden and its role in prognosis, especially when combined with clinicoradiological factors, remain to be further defined.

We analyzed 103 patients with HPV-positive OPSCC enrolled in an observational biomarker study, most of whom received induction chemotherapy or chemoimmunotherapy followed by definitive radiotherapy. Blood samples were collected at pretreatment, post-radiotherapy, and follow-up time points, and ctHPV DNA levels were quantified using droplet digital PCR. Baseline clinicoradiological parameters from contrast-enhanced MR or CT and ¹⁸F-FDG PET/CT were analyzed for their association with ctHPV DNA levels and clinical outcomes.

Baseline ctHPV DNA correlated with primary tumor volume (V_T), nodal volume (V_N), total tumor volume (V_T+N), and the number of involved primary tumor sites and lymph node regions, particularly LN-related features. V_T and maximum LN diameter were independent predictors of baseline ctHPV DNA. Detectable follow-up ctHPV DNA was associated with inferior progression-free survival but showed low sensitivity and positive predictive value for relapse detection. Integrative stratification using baseline ctHPV DNA and V_T+N identified a potential high-risk subgroup with high tumor volume but paradoxically low ctHPV DNA (VOL^highDNA^low). Exploratory RNA-seq analysis was performed to investigate potential biological features underlying this discordance, and a seven-gene signature associated with PFS was identified.

These findings suggest that baseline ctHPV DNA reflects tumor burden and may provide additional information for upfront risk stratification in HPV-positive OPSCC, warranting further validation in larger prospective cohorts.