Inclusion criteria

1) Histologically confirmed colorectal adenocarcinoma.

2) Confirmed measurable disease as per the Response Evaluation Criteria in Solid Tumors (RECIST) version 1.1.

3) No previous chemotherapy except for adjuvant chemotherapy completed 6 months or more before enrollment.

4) Age ≥75 years at the time that informed consent is obtained.

5) Eastern Cooperative Oncology Group (ECOG) performance status of 0 - 1.

6) Patients with expected survival for at least 3 months.

7) Adequate bone marrow reserve and hepatic and renal function―white blood cell count ≥ 3000/mm³, neutrophil count ≥ 1500/mm³, hemoglobin level ≥ 9.0 g/dl, platelet count ≥ 100,000/mm³, serum aspartate aminotransferase ≤ 100 IU, serum alanine transaminase ≤ 100 IU, total bilirubin level ≤ 1.5 mg/dl, serum creatinine level ≤ 1.2 mg/dl and creatinine clearance ≥ 50 ml/min.

8) Normal electrocardiogram.

9) Provision of signed written informed consent.

10) Capability of oral intake.

Exclusion criteria

1) Concurrent treatment with prohibited medications, including phenytoin and flucytosine.

2) Administration contraindication of fluoropyrimidines and bevacizumab.

3) Serious infection.

4) Hepatitis B virus S antigen positive.

5) Active double cancer.

6) Uncontrolled hypertension.

7) Severe comorbidity such as intestinal tract paralysis, ileus, interstitial lung disease, uncontrolled diabetes, heart failure, renal failure, and liver failure.

8) Past history of radiation therapy over the pelvic cavity.

9) Massive pleural effusion or ascites.

10) Severe diarrhea (diarrhea affecting daily life in patients having an artificial anus).

11) Brain metastasis with symptoms.

12) Uric protein ≥ 2+.

13) Men of childbearing potential that do not accept to use an adequate method of contraception or pregnant or lactating women at any time during study.

14) Systemic administration of corticosteroids.

15) Past history of thrombosis, cerebral infarction, cardiac infarction, or pulmonary infarction.

16) History of surgery or biopsy via a great incision within 4 weeks before the registration.

17) Systemic administration of anti-platelet drug (≥325 mg/day) except for the administration for pain.

18) Bleeding disorders including congenital bleeding factor, clotting disorder (prothrombin time-international normalized ratio ≥1.5 within 2 weeks before the registration), or anti-coagulation drug.

19) Severe mental illness.

20) Judged inappropriate for the entry into the study by the investigator.