Atezolizumab Before Surgery for the Treatment of Regionally Metastatic Head and Neck Squamous Cell Cancer With an Unknown or Historic Primary Site

Inclusion Criteria: * Participants with biopsy proven, surgically resectable head and neck cutaneous squamous cell carcinoma regionally metastatic to lymph nodes in the head and/or neck with a historical or unknown (but not concurrent) primary site * Patients must be \>= 18 years * Patients with resectable regionally metastatic HNCSCC from an unknown or historical primary and no evidence of distant metastatic disease * Full decision-making capacity and consent provided and documented * Radiographically measurable disease per immune Response Evaluation Criteria in Solid Tumors (iRECIST) * Surgically resectable disease per standard of care (SoC) * For Women of childbearing potential: agreement to remain abstinent (refrain from heterosexual intercourse) or use contraceptive methods as defined below: \* Women must remain abstinent or use contraceptive methods with a failure rate of \< 1% per year during the treatment period and for 5 months after the final dose of atezolizumab \* A woman is considered to be of childbearing potential if she is postmenarchal, has not reached a postmenopausal state (\>= 12 continuous months of amenorrhea with no identified cause other than menopause), and has not undergone surgical sterilization (removal of ovaries and/or uterus). The definition of childbearing potential may be adapted for alignment with local guidelines or requirements \* Examples of contraceptive methods with a failure rate of \< 1% per year include bilateral tubal ligation, male…