Inclusion Criteria:

          -  Provided written informed consent for treatment.

          -  Age ≥ 20 years old

          -  Meet at least one of the following requirements; A. PD-L1 positive by IHC or B. EBV
             positive by ISH or C. MSI-H by IHC or D. POLE mutation E. POLD1 mutation

          -  Progressive disease who failed to previous standard treatment

          -  At least one measurable lesion according to Response Evaluation Criteria in Solid
             Tumors (RECIST) version 1.1 criteria

          -  Eastern Cooperative Oncology Group (ECOG) performance status 0 or 1 on time of
             patient's allocation.

          -  Adequate organ function as defined by the following criteria:

        A. Adequate hematological function defined by absolute neutrophil count (ANC) ≥ 1500/mm3,
        platelet count ≥ 100,000/mm3 , hemoglobin ≥ 9.0 g/dL B. Adequate hepatic function defined
        by AST and ALT levels ≤ 2.5 × upper limit of normal (ULN) and total bilirubin level ≤ 1.5 ×
        ULN C. Adequate renal function defined by and estimated creatinine clearance (CrCl) ≥ 30
        mL/min (MDRD)

          -  A life expectancy of at least 90 days

          -  Negative serum pregnancy test at screening for women of childbearing potential

          -  Highly effective contraception for both male and female subjects if the risk of
             conception exists.

        Exclusion Criteria:

          -  Previous treatment with immune checkpoint inhibitor (Anti-PD1, Anti-PDL1, Anti-CTLA4
             etc.)

          -  Known severe hypersensitivity reactions to monoclonal antibodies (Grade ≥ 3 NCI CTCAE
             v 4.03), any history of anaphylaxis, or uncontrolled asthma (that is, 3 or more
             features of partially controlled asthma)

          -  Prior organ transplantation, including allogeneic stem cell transplantation

          -  Significant acute or chronic infections

          -  Active autoimmune disease that might deteriorate when receiving an immunostimulatory
             agent:

          -  All subjects with brain metastases, except those meeting the following criteria:

          -  Subjects with clinically significant (i.e., active) cardiovascular medical history:
             cerebral vascular accident/stroke (< 6 months prior to enrollment), myocardial
             infarction (< 6 months prior to enrollment), unstable angina, congestive heart failure
             (≥ New York Heart Association Classification Class II), or serious cardiac arrhythmia
             requiring medication

          -  Unresolved toxicity of Grade >1 attributed to any prior therapies (excluding alopecia,
             skin pigmentation and anemia).

          -  Pregnancy or lactation

          -  Interstitial lung disease

          -  Known alcohol or drug abuse

          -  All other significant diseases (for example, inflammatory bowel disease, uncontrolled
             asthma), which, in the opinion of the Investigator, might impair the subject's
             tolerance of trial treatment

          -  Any psychiatric condition that would prohibit the understanding or rendering of
             informed consent

          -  Vaccination within 4 weeks of the first dose of avelumab and while on trial is
             prohibited except for administration of inactivated vaccines