Inclusion Criteria:

          -  Male or female, age 18 years or older.

          -  Willingness to provide written informed consent for the study.

          -  Has baseline tumor biopsy specimen available or willingness to undergo a pretreatment
             tumor biopsy to obtain the specimen.

          -  Eastern Cooperative Oncology Group (ECOG) performance status of 0 to 1.

          -  For Part 1a: Subjects with histologically or cytologically confirmed advanced or
             metastatic solid tumors that have failed prior standard therapy (including subject
             refusal or intolerance).

          -  For Part 1b: Subjects with histologically or cytologically confirmed advanced or
             metastatic endometrial cancer, gastric cancer, melanoma, microsatellite unstable
             (MSI) colorectal cancer or other MMR-deficient tumors, non-small cell lung cancer,
             renal cell carcinoma, head and neck squamous cell carcinoma, triple negative breast
             cancer, pancreatic ductal carcinoma, or transitional cell carcinoma of the
             genitourinary tract that have had disease progression after available therapies for
             advanced or metastatic disease that are known to confer clinical benefit, been
             intolerant to treatment, or refused standard treatment.

          -  For Part 1b: Must have documented confirmed disease progression on a prior PD-1
             pathway targeted agent or must be PD-1 pathway-targeted treatment naïve.

          -  For Part 2: Subjects with histologically or cytologically confirmed advanced or
             metastatic SCLC. Must not have had previous treatment with antibodies that modulate
             T-cell function or checkpoint pathways. Must have disease progression on or after
             platinum-based chemotherapy or must be intolerant to or refuse standard treatment.
             Must not have received more than 2 lines of prior therapy.

        Exclusion Criteria:

          -  Laboratory parameters not within the protocol-defined range.

          -  Receipt of anticancer medications or investigational drugs within a defined interval
             before the first administration of study drug.

          -  Received an immune-suppressive based treatment for any reason within 14 days prior to
             the first dose of study treatment.

          -  Has not recovered from toxic effect of prior therapy to < Grade 1.

          -  Active or inactive autoimmune process.

          -  Has received a live vaccine within 30 days of planned start of study therapy.

          -  Active infection requiring systemic therapy.