Inclusion Criteria:

          1. Has advanced, metastatic or unresectable GI tract tumors that are refractory or
             intolerant to existing available therapies and for whom the investigator recommends
             fluoropyrimidine monotherapy.

          2. Has measurable disease in accordance with Respond Evaluation Criteria in Solid Tumors
             (RECIST) guidelines (Version 1.1).

          3. Is aged ≥18 years

          4. Has not received treatment with intravenous (IV) 5 FU or oral 5 FU analogs in the 4
             weeks preceding enrollment

          5. Has Eastern Cooperative Oncology Group (ECOG) Performance Status of 0-2 at study entry

          6. Has adequate bone marrow, liver, and renal function as assessed by the following
             laboratory requirements conducted within 7 days before starting study treatment:

               1. peripheral ANC of ≥1.5 × 109/L

               2. platelet count of ≥75 × 109/L without growth factor/transfusion

               3. hemoglobin ≥8.5 g/dL without growth factor/transfusion

               4. estimated glomerular filtration rate >50 mL/min

               5. total bilirubin <2 × upper limit of normal (ULN); <5 × ULN if patient has liver
                  metastases, biliary tract cancer; or ≤3 × ULN if the patient has Gilbert's
                  disease

               6. Aspartate aminotransferase (AST) or alanine aminotransferase (ALT) <2.5 × ULN,
                  with liver metastasis <5 × ULN

               7. international normalized ratio (INR) <1.5

          7. Has a life expectancy of at least 12 weeks

          8. Female patients of childbearing potential and male patients with partners capable of
             reproduction must agree to use an effective contraceptive method from the time of
             Screening through 60 days after the last dose of capecitabine

          9. Females of childbearing potential must have a negative serum pregnancy β human
             chorionic gonadotropin pregnancy test result

         10. Willingly provides written, informed consent.

         11. Has resolution or stabilization of acute toxicity from prior therapy to Grade <2 -
             except Grade 2 neuropathy

         12. If patient has human immune deficiency virus (HIV) infection, it is controlled with
             undetectable viral load with antiretroviral treatment.

         13. If patient has hepatitis C infection and received antiviral treatment, has a negative
             viral load at Screening

         14. If patient has chronic hepatitis B infection and is receiving antiviral treatment, has
             a negative viral load at Screening.

         15. Is willing and able to comply with all protocol required visits and assessments

        Exclusion Criteria:

          1. Is unable to take oral medication or malabsorption syndromes potentially interfering
             with medication absorption (e.g., short bowel syndrome or chronic, partial bowel
             obstruction)

          2. Has history or presence of clinically significant abnormal 12 lead ECG results, in the
             investigator's opinion

          3. Has current brain metastasis

          4. Has prolonged QTc (with Fridericia's correction) of >480 msec in men and women
             performed at Screening

          5. Has a history of prolonged QTc interval, ventricular tachycardia/fibrillation or
             significant ventricular arrhythmia, or Torsades de Pointes, or a history of
             ventricular ablation for arrhythmia

          6. Has congenital long QT syndrome or a family history of long QT syndrome

          7. Has other clinically significant cardiac disease including, but not limited to,
             uncontrolled angina, myocardial ischemia or infarction within 6 months, congestive
             heart failure >Class II per the New York Heart Association, or history of myocarditis

          8. Has an electrolyte disturbance, such as uncorrected hypokalemia/hyperkalemia,
             hypomagnesemia, or hypocalcemia. Patients can be enrolled following successful
             correction of an electrolyte disturbance.

          9. Is currently using any drugs included in the prohibited medications list in the
             protocol (including those that can prolong QTc) that cannot be discontinued

         10. Has known hypersensitivity to any of the components of study treatments

         11. Has other primary cancer requiring treatment within the last 3 years, except for
             cervical intraepithelial neoplasia, ductal carcinoma in situ, or completely excised
             squamous or basal cell carcinoma

         12. Is a pregnant or lactating female

         13. Had major surgery, open biopsy, or significant traumatic injury within 4 weeks prior
             to the first dose of study treatment

         14. Is receiving or has received any investigational treatment within 4 weeks prior to
             study entry, or participating in another clinical study

         15. Has known DPD deficiency