880P ctHPV16-DNA in Liquid Biopsy: A promising biomarker to monitor disease status in patients with HPV-positive oropharyngeal squamous cell carcinoma

Globally the incidences of oropharyngeal squamous cell carcinoma (OPSCC), especially those associated with high-risk human papillomavirus are rising. Although patients with HPV-positive OPSCC present with better survival, up to 25% develop recurrent disease. Biomarkers to monitor therapy response, minimal residual disease and tumor burden during follow-up are urgently needed. The detection of cell-free (cf)HPV-DNA in blood plasma offers the opportunity for minimally invasive disease monitoring and early recurrence detection. We examined 34 patients with HPV-related OPSCC and 21 controls (healthy donors and HPV-negative OPSCC patients) to investigate cfHPV16-DNA status prior to and during therapy as well as throughout follow-up. qPCR and ddPCR were applied to quantify the concentration of cfHPV16-DNA in plasma, using the viral gene E6 as a target. No cfHPV16-DNA or <10 copies per ml plasma were detected in healthy donors or HPV-negative OPSCC patients. Plasma samples from patients with HPV-positive OPSCC collected prior to treatment. At the cut-off of 10 copies/ml plasma, ddPCR showed 79% sensitivity, 80% specificity, 70% NPV, and 90% PPV, whereas qPCR showed 73% sensitivity, 80% specificity, 60% NPV, 90% PPV. Patients without clinical evidence of recurrence had significantly lower cfHPV16-DNA concentrations after therapy, whereas increase of copy number was correlated to recurrent disease. Our results demonstrate that ddPCR is a more sensitive method compared to qPCR for detection of cfHPV16-DNA in plasma of patients with HPV16-positive OPSCC. cfHPV16-DNA correlated with tumor burden and therefore presents a promising diagnostic tool. Nevertheless, prospective studies with expanded patient cohorts are necessary to investigate the kinetics of cfHPV16-DNA in relation to therapy response and the development of recurrent and metastatic disease.