Blood and saliva‐derived ctDNA is a marker of residual disease after treatment and correlates with recurrence in human papillomavirus‐associated head and neck cancer

Abstract Background There is an alarming increase in human papillomavirus‐associated head and neck cancer (HNC), reaching epidemic levels. While patient prognosis is generally good, off‐target treatment effects are associated with decreased quality of life. Thus, non‐invasive strategies to predict treatment response and risk of recurrence could help de‐escalate treatment. In this study, we tested circulating tumor (ct)DNA in liquid biopsies (blood/saliva) of HPV‐positive HNC patients to assess treatment response and disease progression. Methods A total of 235 blood and saliva samples were collected from 60 HPV‐positive and 17 HPV‐negative HNC patients (control group) before and/or after treatment. Samples were analyzed using ddPCR for HPV16/18/31/33/35/45 and correlated with imaging and pathological examination. Results HPV‐ctDNA detection was significantly higher prior to treatment (91%) than after treatment (8.0%) (χ2 p