Inclusion Criteria:

          -  Participants must be ≥ 18 years old.

          -  Participants with SCCHN or mCRCP.

          -  Participants must have histological diagnosis of solid tumors and provide tumor
             tissue.

          -  Measurable disease by RECIST v1.1 with at least 1 measurable lesion.

          -  Eastern Cooperative Oncology Group (ECOG) Performance Status (PS) 0 or 1.

          -  Adequate bone marrow, renal and liver function

          -  Highly effective contraceptive use by men with the ability to father a child or women
             of childbearing potential.

          -  A WOCBP must have a negative highly sensitive pregnancy test ([urine or serum] as
             required by local regulations) at C1D1.

          -  Signed and dated informed consent.

        Exclusion Criteria:

          -  Known prior severe hypersensitivity to investigational products or any component in
             their formulations, including known severe hypersensitivity reactions to monocolonal
             antibodies.

          -  Known history of: immune-mediated colitis, inflammatory bowel disease, pneumonitis, or
             pulmonary fibrosis.

          -  Active or prior autoimmune disease that might deteriorate when receiving an
             immunostimulatory agent.

          -  Prior organ transplantation including allogenic stem cell transplantation.

          -  Vaccination within 4 weeks prior to C1D1 and while on trial is prohibited except for
             administration of inactivated vaccines.

          -  Known symptomatic brain lesions requiring steroids.

          -  Known history of testing positive for human immunodeficiency virus (HIV or known
             acquired immunodeficiency syndrome (AIDS).

          -  Positive HBV surface antigen or HCV test indicating acute or chronic infection..

          -  Active infection requiring systemic therapy

          -  Clinically significant (i.e., active) cardiovascular disease including the following:
             documented left ventricular ejection fraction (LVEF) <50% by ECHO/MUGA; cerebral
             vascular accident/stroke or transient ischemic attack; myocardial infarction; unstable
             angina; congestive heart failure or serious cardiac arrhythmia (uncontrolled,
             clinically significant) requiring medication.

          -  Diagnosis of any other malignancy within 2 years prior to C1D1, except for adequately
             treated basal cell or squamous cell skin cancer, carcinoma in situ of the breast,
             bladder or of the cervix and for Combination A only, low-grade (Gleason 6 or below)
             prostate cancer on surveillance with no plans for treatment intervention (e.g.,
             surgery, radiation, or castration) or adequately treated prostate cancer.

          -  Current use of immunosuppressive medication at the time of study enrollment.

          -  Major surgery within 4 weeks prior to study enrollment.

          -  Conditions that may impair intake or absorption such as inability to swallow capsules
             or tablets; known malabsorption syndrome; or baseline diarrhea ≤ Grade 1.

          -  Participation in other studies involving investigational drug(s) within 2 weeks prior
             to C1D1.