Salivary HPV DNA informs locoregional disease status in advanced HPV-associated oropharyngeal cancer

Objectives: Quantifying tumor DNA in tissue and circulating in blood permits high-quality molecular monitoring to detect and track cancer progression. Evaluating tumor DNA in both blood and saliva in human papillomavirus (HPV)-associated oropharyngeal cancer (OPC) could provide a non-invasive and clinically actionable method for real-time disease detection. Methods: We previously validated an ultrasensitive droplet-digital (dd) PCR assay targeting the dominant high-risk HPV subtypes causally linked to OPC. Here we enrolled an observational cohort to evaluate the predictive and prognostic potential of paired plasma-salivary tumor DNA among 21 patients with advanced HPV+OPC. Results: In patients with recurrent, persistent locoregional (LR) disease, median baseline normalized salivary HPV DNA was 10.9 copies/ng total DNA, nearly 20x higher compared with those with distant disease only (p=0.01). A cutoff of 5 copies/ng yielded 87% sensitivity and 67% specificity for accurately predicting LR disease. Total tumor burden among those with LR disease strongly correlated with salivary HPV DNA levels (R=0.83, p=0.02). The rise and fall of salivary HPV DNA predicted treatment failure and response, respectively, in all patients with LR disease, and predated imaging findings. Among paired salivary-plasma (cell-free) cfDNA samples, only higher plasma HPV cfDNA levels were associated with poor outcomes (p<0.01), suggesting that each bodily fluid provides unique information about HPV disease status. Conclusions: Salivary HPV DNA provides valuable information about tumor burden and predicts treatment response in advanced HPV + OPC. Paired blood-saliva samples could be used to monitor HPV DNA with broad applications to inform diagnosis, prognosis, and surveillance in HPV-associated diseases.