Inclusion Criteria:

          1. Patients who have been histopathologically diagnosed with colorectal adenocarcinoma

          2. Patients who have undergone radical curative resection of the primary and metastatic
             tumors

          3. Patients with colon cancer of Stage III based on final findings (T any N1/2 M0) (UICC
             TNM Classification, 8th Edition) who have a past history of standard postoperative
             chemotherapy

          4. Patients who tested positive for ctDNA by an analysis of blood samples using
             SignateraTM within 2 months prior to enrollment

          5. Patients with no obvious relapse confirmed by chest, abdominal, and pelvic CT scans,
             etc.

          6. Patients who are capable of oral ingestion

          7. Patients aged 20 years or older at the time of informed consent

          8. Patients with an Eastern Cooperative Oncology Group (ECOG) performance status (PS) of
             0 or 1

          9. Patients who have no severe disorder in major organs (such as the bone marrow, heart,
             lungs, liver, and kidneys) and meet the following criteria (Data obtained most
             recently and within 14 days of the date of enrollment will be used for enrollment.
             Data obtained 2 weeks before the date of enrollment, on the same day of the week as
             the enrollment date, may be used for enrollment.)

               -  Neutrophil count ≥ 1,500/mm3

               -  Platelet count ≥ 100,000/mm3

               -  Hemoglobin ≥ 8.0 g/dL

               -  Serum creatinine ≤ 1.5 mg/dL

               -  Total bilirubin < 1.5 mg/dL

               -  ALT and AST ≤ 100 U/L

         10. Patients with no diarrhea or stomatitis of Grade 2 or severer according to Common
             Terminology Criteria for Adverse Events (CTCAE) v5.0

         11. Patients who voluntarily gave written consent to participate in the trial after
             receiving a thorough explanation of the trial before enrolling in the trial

        Exclusion Criteria:

          1. Patients with a history of treatment with FTD/TPI

          2. Patients with a history of treatment with 2 or more regimens of postoperative adjuvant
             chemotherapy (Preoperative chemotherapy will not be counted as a regimen.)

          3. Patients with a past history of a malignant tumor

          4. Patients with a local or systemic active infection requiring intervention

          5. Patients who are positive for HBs antigen or positive for HCV antibody

          6. Patients who are positive for HIV antibody (Patients who have not been tested for HIV
             antibody may be enrolled.)

          7. Patients with poorly controlled infections or diabetes

          8. Patients with a past history of interstitial lung diseases (such as interstitial
             pneumonia and pulmonary fibrosis) requiring treatment or extensive findings of these
             diseases on CT

          9. Patients with a serious complication

         10. Patients who have been receiving systemic administration (oral or intravenous) of
             steroids (for 2 weeks or more at a dose of the equivalent of ≥ 10 mg/day of
             prednisolone)

         11. Patients for whom enrollment in the trial is difficult because of clinically
             problematic psychiatric disorders

         12. Pregnant or lactating women

         13. Patients with reproductive potential who do not wish to use adequate contraceptive
             measures during the period of participation in the trial and during the contraception
             period

         14. Patients who are judged by the attending physician to be ineligible for enrollment in
             the trial for other reasons