Key Inclusion Criteria:

          -  Male and female adult patients 18 years of age or older on day of signing informed
             consent.

          -  Patients must have a histologically confirmed advanced, metastatic, or progressive
             Microsatellite Stable (MSS) Colorectal Cancer (CRC) per institutional standards.

          -  Patient has received at least two prior lines of therapy for advanced or metastatic
             CRC, at least one of which included fluorouracil.

          -  Highly effective birth control.

          -  Measurable disease.

          -  Accessible tumor that can be safely accessed for multiple core biopsies and patient is
             willing to provide tissue from newly obtain biopsies before and during treatment.

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

          -  Adequate organ function.

          -  Able to swallow and absorb oral tablets.

        Key Exclusion Criteria:

          -  Prior therapy with an anti-PD-1, anti-PD-L1, or anti-PD-L2 agent or with an agent
             directed to another stimulatory or co-inhibitory T-cell receptor

          -  Current use of NSAIDs, COX-2 inhibitors and aspirin products within 3 days (preferably
             7 days) before treatment initiation or at anytime during the study unless used for
             management of AE.

          -  History of severe hypersensitivity reactions to chimeric or humanized antibodies

          -  Has received prior systemic anticancer therapy including investigational agents within
             4 weeks prior to treatment, or 5 half-lives, whichever is shorter.

          -  Diagnosis of immunodeficiency or is receiving chronic systemic steroid therapy (in
             dosing exceeding 10 mg daily of prednisone equivalent) or any other form of
             immunosuppressive therapy within 7 days prior the first dose of study drug.

          -  Known additional malignancy that is progressing or has required active treatment
             within the past 3 years.

          -  Known active CNS metastases and/or carcinomatous meningitis.

          -  Active autoimmune disease that has required systemic treatment in past 2 years.

          -  History of non-infectious pneumonitis that required steroids or has current
             pneumonitis.

          -  Active infection requiring systemic therapy.

          -  Recent (within the last 12 months) or current GI ulcer, colitis or non-immune colitis.

          -  Known history of human immunodeficiency virus (HIV) infection, Hepatitis B, or active
             Hepatitis C virus infection.

          -  Clinically significant (i.e. active) cardiovascular disease

          -  Allogeneic tissue/solid organ transplant

          -  Medical conditions requiring concomitant administration of strong CYP3A4 or P
             glycoprotein inhibitors or inducers.