Abstract 452: Salivary HPV cell free DNA levels predict locoregional disease burden and response in oropharyngeal cancer
Authors: Hanna Glenn J. , Lau Christie J. , Mahmood Umair , Haddad Robert I. , Paweletz Cloud P. , Janne Pasi A. 
Published: August 2019

Abstract
Purpose: The human papillomavirus (HPV) is linked to the majority of oropharyngeal squamous cell carcinomas (OPSCC). We have previously shown that tumor-derived HPV cell-free (cf)DNA can be detected and quantified in circulation with high sensitivity and specificity using droplet digital (dd)PCR1. Further, we have shown that plasma cfDNA levels correlate with disease burden and indicate treatment response in advanced OPSCC. In this study we pair plasma with salivary HPV cfDNA to understand its clinical application in monitoring locoregional spread of disease.
Methods: We present a proof-of-concept prospective observational cohort of recurrent, metastatic (R/M) HPV+ OPSCC patients treated with standard systemic therapies or on active surveillance. We utilized ultrasensitive ddPCR to identify and quantify both plasma and salivary HPV cfDNA (subtypes 16, 18, 31, 33 and 45) at multiple time points. Salivary HPV cfDNA was normalized to total DNA concentration as measured by fluorometric quantification. We then compared matched plasma and normalized salivary HPV cfDNA concentrations at various timepoints with clinical parameters, such as tumor burden and therapeutic response.
Results: Clinicopathologic data from 15 R/M patients revealed a male cohort with a median age of 57 at diagnosis. Five (33%) were on immunotherapy and 6 (40%) on standard chemotherapy during the study period (3 months). Salivary HPV cfDNA was detected in 13/15 (87%) samples (range 0-729 copies/mL) in at least one timepoint during the study (plasma cfDNA was detected in 12/15 or 80% of the cohort, range 0-12,949 copies/mL). All patients with measurable locoregional (LR) disease had detectable salivary cfDNA. While matched plasma and salivary cfDNA levels showed no correlation among individual patients, plasma cfDNA levels correlated with site of disease (LR, pulmonary or extra-pulmonary) (p &lt; 0.001), while median salivary cfDNA levels strongly correlated with LR tumor burden (R = 0.81, p &lt; 0.001). Salivary cfDNA levels declined by 80% of their baseline value within a median of 6.5 days among all patients with LR disease experiencing a response to treatment.
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Conclusion: Our results suggest that high sensitivity salivary HPV cfDNA levels correlate with locoregional disease burden and can be an early indicator of locoregional treatment response, while our prior work has supported the role of plasma HPV cfDNA levels in monitoring metastatic disease. Evaluating paired plasma and salivary HPV cfDNA levels in a curative HPV OPSCC population is underway to further validate their prognostic and predictive potential.
1Hanna GJ, Supplee JG, Kuang Y, Mahmood U, Lau CJ, Haddad RI, et al. Plasma HPV cell-free DNA monitoring in advanced HPV-associated oropharyngeal cancer. Ann Oncol. 2018;29:1980–6.
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Citation Format: Glenn J. Hanna, Christie J. Lau, Umair Mahmood, Robert I. Haddad, Cloud P. Paweletz, Pasi A. Janne. Salivary HPV cell free DNA levels predict locoregional disease burden and response in oropharyngeal cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 452.