Circulating cell free HPVDNA in HPV positive head and neck cancer reveals fast responders and early peakers during treatment

The incidence of human papillomavirus-positive (HPV⁺) head and neck cancer (HNC), particularly oropharyngeal squamous cell carcinoma (OPSCC), is rising globally. Although radio- or chemo-radiotherapy yields better outcomes for patients with HPV⁺ tumors compared to those with HPV-negative tumors, these treatments do not cure all cases and are associated with significant side effects. This underscores the need for more personalized therapy. To help individualize treatment, we evaluated the presence of cell-free HPV DNA (cfHPV-DNA) in plasma collected before, during, and after therapy in patients with HPV⁺ HNC and correlated cfHPV-DNA levels with clinical characteristics, HPV genotype, and treatment response. 267 longitudinal plasma samples were collected from 83 patients with HPV⁺ HNC/cancer of unknown primary, at diagnosis/recurrence, during treatment and follow-ups, and tested for cfHPV-DNA with droplet digital PCR assaying for HPV16, 18, 33 or 35.39. 76/81 (93.8%) eligible diagnostic or recurrence samples tested positive for cfHPV-DNA, while a diagnostic sample was unavailable/or had inadequate cfDNA in 2/83 cases. cfHPV-DNA levels declined in most patients by 3-4 weeks post-radiotherapy initiation and became undetectable (fast responders) in approximately 30% of cases. By 3-6 months post-treatment, most patients had no detectable cfHPV-DNA. To date, no new recurrences have been documented, although two patients were unresponsive to therapy. Most HPV⁺ OPSCC patients were cfHPV-DNA-positive at diagnosis and cleared their cfHPV-DNA upon treatment, but the speed of clearance varied depending on tumor sub-site, patient characteristics and treatment. The data suggest that follow-up with cfHPV-DNA is a promising clinical approach and should be expanded to include more patients and longer time periods.