SURVEILLE-HPV: Evaluation of HPV16 Circulating DNA as Biomarker to Detect the Recurrence, in Order to Improve Post Therapeutic Surveillance of HPV16-driven Oropharyngeal Cancers

Inclusion Criteria: 1. Patient aged 18 years or over 2. Patient with p16 positive Oropharyngeal squamous cell carcinoma (OPSCC) 3. Clinical stage T1-4, N0-3, M0 (stages I-III) 4. Any tobacco status 5. Life expectancy greater than 36 months 6. Positive HPV16 Ct-DNA measured before curative anticancer treatment 7. Treated by any curative treatment 8. Complete response at 3 months after end of treatment, which means: * Undetectable HPV16 Ct-DNA and no residual disease on imaging (group A) or * Undetectable HPV16 Ct-DNA and suspicious imaging but persistent disease excluded by either biopsy or repeated imaging (group B1) or * Positive HPV16 Ct-DNA and no residual disease on imaging but negative HPV16 Ct-DNA on the subsequent assessment. This second test will be done 1-2 months after the first one (group C1). 9. Patient must be affiliated to a Social Security System (or equivalent) 10. Patients must have signed a written informed consent form prior to any trial specific procedures. If the patient is physically unable to give his/her written consent, a trusted person of his/her choice, note related to the investigator or the sponsor, can confirm in writing the patient's consent. Exclusion Criteria: 1. Uncontrolled intercurrent illness that would limit compliance with study requirements. 2. Active invasive malignancy within 3 years of inclusion except for non-invasive malignancies such as non-melanomatous carcinoma of the skin or ductal carcinoma in situ of the breast that has/have been surgically cured. 3. Any other HPV induced cancer within 5 years 4. Any condition that may jeopardize the patient participation as well as non-contraception for male and female with child-bearing potential, pregnancy or breast-feeding 5. Patient unwilling or unable to comply with the study protocol and follow-up schedule. 6. Participation in another clinical trial with an investigational medical product during the last 30 days prior to the inclusion and during the present study (except if patient is included in the control arm, with placebo or with a product that have a marketed authorization, used as per the summary of product characteristics (SmPC) for the given indication). 7. Patient deprived of liberty or placed under protective custody or guardianship.