First aim was to compare ddPCR assays of ctHPVDNA with p16 IHC and qualitative HPV PCR. Second aim was to carry out longitudinal blood sampling to test for association of ctHPVDNA with histological confirmed recurrence. Third aim was to perform a multidimensional assessment which included: (1) clinical features; (2) ctHPVDNA; (3) MRI-based tumor size measurements of primary tumor (PT) and cervical lymph node metastases (CLNM).

Plasma samples were collected before treatment and during follow-up, and ddPCR assay comprising E6 of HPV16 and HPV 33 and HPV 35 was used.

Present study was conducted at diagnosis in 117 patients and revealed a ctHPVDNA sensitivity of 100% (95% CI 95.5-100) and a specificity of 94.4 (95% CI 81.3-99.3), positive predictive value (PPV) of 94.4 (95% CI 81.3-99.3), and negative predictive value (NPP) of 100% (95% CI 89.7-100). During follow-up ctHPVDNA had a sensitivity of 100% (95% CI 72.1-100)% and specificity of 98.4% (95% CI 91.7-100)%, PPV% of 90.9% (95% CI 62.3-98.4) and NPV% of 100% (95% CI 94.3-100) for ability to detect recurrence. Correlation between both the CLNM volume and the sum of PT and CLNM volume was observed.

ctHPVDNA was superior to p16 in identification of HPV-OPSCC at diagnosis. Introduction of ctHPVDNA, beyond diagnostic setting, represents a great opportunity to improve follow-up protocol of OPSCC patients.