Phase 1 Study of BAY1905254 - An Early Clinical Research Study to Evaluate a New Drug Called Bapotulimab (BAY1905254) in the Expansion Cohort in Combination With Pembrolizumab in Head and Neck Cancer That Has Returned or is Discovered to be Metastatic and is Expressing PDL1.

Main Inclusion Criteria: * Male or female patients aged ≥ 18 years. * Eastern Cooperative Oncology Group (ECOG) performance status of 0 to 1. * Patients must have measurable disease (at least one unidimensional measurable lesion by Computed tomography \[CT\] or Magnetic resonance imaging \[MRI\]) per Response evaluation criteria in solid tumors (RECIST) 1.1, and following histologically confirmed, advanced or metastatic solid tumors: * Dose escalation: All solid tumor types with a likelihood of sensitivity to immunotherapy, as judged by the investigator. * Expansion of Bapotulimab in combination with pembrolizumab in Head and neck squamous cell carcinoma (HNSCC): recurrent or metastatic head and neck squamous cell carcinoma IO-naïve PDL1+/ CPS≥1(PD-L1: Programmed death ligand 1; CPS: Combined positive score). * Provision of archival tumor tissue at screening is mandatory for all patients in dose escalation. * For dose escalation, patients: must have received standard therapy or have no standard therapy available or patients have actively refused any treatment which would be regarded standard. Or in the opinion of investigator have been considered ineligible for a particular form of standard therapy on medical grounds. * Adequate bone marrow, liver and renal function. * Adequate cardiac function, measured by echocardiography. Main Exclusion Criteria: * History of severe immune related adverse effects from prior immunotherapy (CTCAE v.5.0 Grade 4; CTCAE v.5.0 Grade 3 requiring treatment \> 4 weeks), except hypothyroidism clinically stable on hormone replacement treatment and controlled type 1 diabetes. * Severe (CTCAE v.5.0 Grade ≥ 3) infections within 4 weeks before the first study drug administration, including but not limited to hospitalization for complications of infection, bacteremia, or severe pneumonia. Clinically active infections (CTCAE v.5.0 \> Grade 1) within 2 weeks before the first study drug administration. * Previous or active myocarditis/myositis in history (independent of cause) * Active or history of autoimmune disease. * Known human immunodeficiency virus (HIV) infection. * Active hepatitis B virus (HBV) or hepatitis C virus (HCV) infection. * Treatment with systemic immunosuppressant medications within 2 weeks before the first study drug administration. * Ongoing or previous anti-cancer treatment or any immunostimulatory treatment including but not limited to interferons (IFNs), interleukin (IL)-2 and agonists for members of the tumor necrosis factor (TNF) receptor superfamily (e.g. 4-1BB) within 4 weeks before the first study drug administration. * For dose expansion cohort of Bapotulimab in combination with pembrolizumab in HNSCC: has progressive disease (PD) within six (6) months of completion of curatively intended systemic treatment for locoregionally advanced HNSCC.