Inclusion criteria

18 years of age or older Histologically or cytologically verified, inoperable locally recurrent or metastatic SCAC No prior systemic therapy other than the following: •Chemotherapy administered concomitantly with radiotherapy as a radiosensitizing agent •Prior neoadjuvant or adjuvant therapy if completed ≥6 months before study entry Measurable disease per RECIST v1.1 as determined by local site investigator/radiology assessment and after any tissue collected during biopsy Adequate tissue and whole blood sample with the central testing result before randomization Biopsy for archival samples within 9 months before randomization ECOG performance status 0 to 1 If HIV-positive, then must be stable as defined by: •CD4+ count ≥200/μl •Undetectable viral load per standard of care assay •Receiving antiretroviral therapy (ART/HAART) for at least 4 weeks before study enrollment and have not experienced any HIV-related opportunistic infection for at least 4 weeks before study enrollment