Inclusion Criteria:  Participants must have histologically or cytologically confirmed incident or recurrent squamous cell carcinoma of the tonsil or base of tongue (oropharynx) - includes biopsy of any lymph node with clinical evidence of an oropharynx tumor (unknown primary carcinoma in an involved cervical neck lymph node is permitted if high-risk HPV testing is positive on the involved node) HPV-associated tumor as defined by one or more : positive p16 immunohistochemistry (>70%) OR in situ hybridization OR PCR-based methods Age 18 years or older Will undergo oropharyngeal cancer treatment with curative intent Ability to understand and the willingness to sign a written informed consent document. Baseline positive or detectable ctHPV DNA result prior to treatment  Exclusion Criteria:  Distant metastatic disease (M1, AJCC 8th edition) Undetectable ctHPV DNA result at baseline