Inclusion Criteria:

          1. Has provided written informed consent.

          2. Patient with confirmed histologically proven metastatic or locally advanced
             colorectal adenocarcinoma who are MSS (ie, not MSI) based on either an analysis of
             tissue from a prior biopsy or based on tissue from a new biopsy.

          3. Patient with the presence of at least 1 lesion with measurable disease as defined by
             10 mm in the longest diameter for a soft tissue lesions or 15 mm in the short axis
             for a lymph node by RECIST and irRC criteria for a response assessment.

          4. Patient has received at least 2 prior lines of standard chemotherapies for mCRC and
             is refractory to or failing those chemotherapies.

          5. Age ≥ 18 years.

          6. Eastern Cooperative Oncology Group performance status of 0 to 1

          7. Life expectancy of ≥ 4 months.

          8. Has adequate organ function

          9. Women of childbearing potential must have a negative pregnancy test (urine or serum)
             within 7 days before starting study drugs. Is able to take medications orally

        Exclusion Criteria:

          1. Has a serious illness or medical condition

          2. Treatment with any of the following within the specified time frame before
             enrollment:

               1. Major surgery within the past 4 weeks (the surgical incision should be fully
                  healed before study drug administration).

               2. Any anticancer therapy within the past 3 weeks before enrollment.

               3. Extended field radiation within the past 4 weeks or limited field radiation
                  within the past 2 weeks before enrollment.

               4. Any investigational drug/device received within the past 4 weeks or 5 times the
                  half-life (whichever is shorter) before enrollment.

          3. Previous treatment with TAS-102.

          4. Prior treatment with anti-PD-1, anti- PD-L1, anti programmed cell death ligand 2,
             anti-CD137, anti-OX-40, anti CD40, anti cytotoxic T lymphocyte associated antigen-4
             antibodies, or any other immune checkpoint inhibitors.

          5. Unresolved toxicity of ≥ Common Terminology Criteria for Adverse Events version
             (CTCAE) version 4.03 grade 2 attributed to any prior therapies (excluding anemia,
             alopecia, skin pigmentation, and platinum induced neurotoxicity).

          6. Prior events of immune-mediated pneumonitis, immune-mediated colitis, immune-mediated
             hepatitis, immune-mediated endocrinopathies, immune mediated nephritis and renal
             dysfunction, immune mediated rash, immune mediated encephalitis, and history of
             infusion reactions to nivolumab.

          7. Known or assumed hypersensitivity to TAS-102 or nivolumab or any of its ingredients,
             including polysorbate 80-containing infusion.

          8. Previous severe hypersensitivity reaction to treatment with another mAb.

          9. Pregnant or lactating female.

         10. Inappropriate for entry into this study in the judgment of the investigator.