A Study on Using Cell-Free Tumor DNA (ctDNA) Testing to Decide When to StartRoutine Treatment in People With Human Papilloma Virus (HPV)- Associated Oropharynx Cancer (OPC)

This study will look at whether monitoring HPV ctDNA levels is an effective way to detect cancer relapse risk in people with HPV-OPC. All participants will have recently had surgery to treat their disease, or they will be scheduled to have this surgery. In Arm A the researchers will see whether monitoring participants' HPV ctDNA levels can safely identify patients who do not need radiation therapy (RT) after surgery and whose RT can be delayed until their HPV ctDNA levels become detectable. In Arm B, the researchers will see whether patients who usually need 6-6.5 weeks of CRT can be selected by HPV ctDNA to receive 3 weeks of CRT.