Inclusion Criteria:

          -  Pathologically-confirmed, locally advanced or metastatic solid tumors that have
             relapsed or are refractory to or are not considered medically suitable to receive
             standard of care treatment (Dose Escalation Phase)

          -  Histologically-diagnosed, advanced Gl tumors that have relapsed or are refractory to
             or are not considered medically suitable to receive standard of care treatment (Dose
             Expansion Phase)

          -  Histologically-diagnosed advanced colorectal tumors that have relapsed or are
             refractory to or are not considered medically suitable to receive standard of care
             treatment (Phase 1b)

          -  Previous enrollment in Dose Escalation or Dose Expansion Phase with documented disease
             progression while on single agent CGX1321 (Roll-over Cohort)

          -  Radiologically measurable disease

          -  Minimum life expectancy of 3 months

          -  Age 18 years or older

          -  Adequate organ function

          -  Recovery from prior treatment-related toxicities

        Exclusion Criteria:

          -  Prior exposure to a WNT inhibitor (except Roll-over cohort)

          -  Prior exposure to an anti-PD-1, anti-PD-L1 or anti-PD-L2

          -  Received previous therapy for malignancy within 21 days

          -  Major surgery within 4 weeks of first dose of study drug

          -  Radiotherapy within 2 weeks of first dose of study drug

          -  Significant GI or variceal bleeding or subdural hematoma within 3 months of the first
             dose of study drug

          -  Known active central nervous system metastases and/or carcinomatous meningitis

          -  Diagnosis of immunodeficiency or is receiving systemic steroid therapy or any other
             form of immunosuppressive therapy within 7 days prior to the first dose of study
             treatment.

          -  Currently receiving medications known to be inhibitors of CYP3A4/5. Subjects currently
             receiving medications of known inducers of CYP3A4/5 or substrates of CYP2C8/9 and
             CYP1A2 may be excluded.

          -  Osteoporosis (T-score of less than -2.5 by DEXA scan)

          -  Bone metastases with prior history of pathologic fracture, lytic lesions requiring an
             orthopedic intervention, or not receiving bisphosphonates or denosumab

          -  History of significant cardiac disease or uncontrolled hypertension

          -  Known history of human immunodeficiency virus (HIV)

          -  Known active hepatitis A, B or C

          -  Known additional malignancy that is progressing or requires active treatment.
             Exceptions include basal cell carcinoma of the skin, squamous cell carcinoma that has
             undergone potentially curative therapy or in situ cervical cancer

          -  Active systemic infection requiring intravenous antibiotics within 2 weeks of
             treatment start

          -  Known psychiatric or substance abuse disorders that would interfere with cooperation
             with the requirements of the study

          -  Pregnancy or lactation

          -  Has had an allogenic tissue/solid organ transplant