Phase 2 Trial of Neoadjuvant and Adjuvant Tiragolumab Plus Atezolizumab in Patients With Newly Diagnosed PD-L1 CPS Positive Resectable Stage 3-4 Oral Cavity Squamous Cell Carcinoma (OCSCC).

Inclusion Criteria: * Signed Informed Consent Form * Age 18 years at time of signing Informed Consent Form * Ability to comply with the study protocol, in the investigator's judgment * Histologically or cytologically confirmed, newly diagnosed, OCSCC that is clinical AJCC 8th edition Stage 3-4 (T1-T4N1-3, T3-T4N0) * Patients with a history of previously resected stage T1N0 or T2N0 OCSCC and no prior history of radiotherapy to the head and neck are eligible at local +/- regional recurrence if they otherwise meet stage criteria. * Surgically resectable OCSCC as determined by the patients' treating head and neck surgeon. Patients with a clinical diagnosis of oral cavity cancer, awaiting a biopsy are eligible to consent for pre-screening. * Measurable disease per RECIST v1.1 * PD-L1 CPS≥ 1 (determined by immunohistochemistry with the 22C3 antibody) as documented through testing of a representative tumor tissue specimen * Availability of a representative tumor specimen for exploratory biomarker research (see Appendix 12 for information on tumor specimens) A formalin-fixed paraffin-embedded (FFPE) tumor specimen in a paraffin block (preferred) or at least 15 slides containing unstained, freshly cut, serial sections must be available for baseline biomarker analysis along with an associated pathology report prior to study enrollment. If archival tumor tissue is unavailable or is determined to be unsuitable for, tumor tissue must be obtained from a biopsy performed at screening. * EC…