Inclusion Criteria:

          1. Male or female participants ≥ 18 years

          2. Must have at least 1 measurable lesion per RECIST v1.1.

          3. Eastern Cooperative Oncology Group (ECOG) performance status score of 0 or 1.

          4. Must have received standard of care, including potentially curative available
             therapies or interventions.

          5. Confirm that an archival tissue sample is available and ≤ 6 months old; if not, a new
             biopsy of a tumor lesion must be obtained. Biopsy must not put participant at undue
             risk and procedure must not be more invasive than a core biopsy.

          6. Adequate organ and marrow function

             Dose escalation only:

          7. Pathologically confirmed non-small cell lung cancer, squamous cell carcinoma of the
             head and neck, renal cell carcinoma, breast cancer, colorectal cancer, melanoma,
             bladder cancer, ovarian cancer, endometrial cancer, Merkel cell carcinoma, or
             gastroesophageal cancer that is metastatic, advanced or recurrent with progression for
             which no alternative or curative therapy exists or standard therapy is not considered
             appropriate by the participant and treating physician (reason must be documented in
             medical records).

             Dose expansion only:

          8. Patients with advanced clear-cell RCC or mCRPC.

          9. Clear-cell RCC patients may have received up to 2 prior lines of therapy, one of which
             must have included an anti-PD-(L)1 based therapy and must not have progressed within
             16 weeks during an anti-PD-(L)1 therapy.

         10. mCRPC patients must have progressed during or following treatment with an androgen
             synthesis inhibitor, and have also had one prior line of a taxane-containing regimen
             or the physician and participant consider the taxane-containing regimen to be
             inappropriate. mCRPC patients must be naive to any immunotherapy (including but not
             limited to anti-PD-(L)1 or anti-CTLA-4 antogonists, sipuleucel-T, etc.).

        Exclusion Criteria:

          1. Use of any live vaccines against infectious diseases (eg, influenza, varicella) within
             4 weeks (28 days) of initiation of investigational product.

          2. Underlying medical conditions that, in the Investigator's or Sponsor's opinion, will
             make the administration of investigational product hazardous (eg, interstitial lung
             disease, active infections requiring antibiotics, recent hospitalization with
             unresolved symptoms) or obscure the interpretation of toxicity determination or AEs,
             or concurrent medical condition requiring the use of immunosuppressive medications or
             immunosuppressive doses of systemic or absorbable topical corticosteroids.

          3. Has known psychiatric or substance abuse disorders that would interfere with
             cooperation with the requirements of the trial.

          4. Is pregnant or breastfeeding or expecting to conceive or father children within the
             projected duration of the study, starting with the pre-screening or screening visit
             through 90 days after the last dose of etrumadenant in combination with zimberelimab.

          5. Any active or documented history of autoimmune disease, or history of a syndrome that
             required systemic steroids or immunosuppressive medications, except for vitiligo or
             resolved childhood asthma/atopy. Participants with asthma who require intermittent use
             of bronchodilators (such as albuterol) will not be excluded from this study.

          6. Prior malignancy active within the previous year except for locally curable cancers
             that have been apparently cured, such as basal or squamous cell skin cancer,
             superficial bladder cancer or carcinoma in situ of the cervix, breast, or prostate
             cancer.

          7. Dose escalation: Prior treatment with an anti-PD-L1, anti-PD-1, anti-CTLA-4, or other
             immune checkpoint inhibitor or agonist as a monotherapy or in combination;

          8. Use of other investigational drugs (drugs not marketed for any indication) within 28
             days or at least 5 half-lives (whichever is longer) before investigational product
             administration.