Trial of Cemiplimab, or Cemip-Chemo Followed by Biomarker-guided Treatment for Pts w/HPV H&N Ca

Inclusion Criteria: * Subjects must have pathologically confirmed HPV-positive head and neck squamous cell carcinoma of the oropharynx. Confirmed HPV-positive disease of other subsites are uncommon but also eligible. * HPV testing must be compliant with the following criteria: * p16 IHC positivity is sufficient to enroll and initiate treatment (p16 IHC interpretation to follow guidelines by Jordan and Lingen et al89). * p16 IHC positivity is to be validated using an HPV nucleic acid based secondary assay (HPV ISH, HPV PCR, HPV cfDNA) before or during the neoadjuvant phase.\* * HPV DNA ISH is acceptable if positive, however a negative HPV DNA ISH should be confirmed by HPV RNA ISH or other nucleic acid based method. * HPV16 type (non-HPV16 related cancers are not eligible)\* * \*In the rare event that a subject starts treatment based on p16 IHC alone and HPV type determination is not yet available, subject may commence neoadjuvant treatment based on p16 IHC alone, as along as HPV nucleic acid testing is pending. Patients with non-HPV16 associated tumors will have to leave the study. Given the prevalence of HPV16 (\~90-95%) and usual rapid turnaround of HPV16 RNA-ISH (other assays) this is not expected, but the primary goal is not to have unnecessary treatment delay for subjects. * Availability of ≥8 unstained 5 micron slides. Subjects who cannot fulfill this requirement will need to undergo a new biopsy prior to enrollment on study. In patients where biopsy is not s…