Colorectal cancer is one of the most common malignant tumors, with the morbidity of approximate 100 million cases per year. About 40% of patients present with metastatic (stage IV) colorectal cancer at the time of diagnosis, and about 25% of patients with local lesion will ultimately develop metastatic disease.

5-Fluorouracil（5-FU) was the only efficacious treatment for metastatic colorectal cancer before the nineties of the 20th century, and afterwards as the discovery of chemotherapy such as oxaliplatin, irinotecan and capecitabine, response rate as well as survival had been improved greatly.

Most of advanced colorectal cancer will progress after first-line treatment; therefore, seeking an efficient and low toxic maintaining regimen to prolong PFS becomes a hot topic in oncologic field. Some clinical researches demonstrated that maintaining treatment followed first-line treating advanced NSCLC could extend PFS and OS. In metastatic colorectal cancer, patients receiving 5-FU/leucovorin(LV) maintaining therapy experienced significantly longer PFS than that stopped chemotherapy after six cycles of FOLFOX4 in OPTIMOX2 study. One phase II study shown that median PFS was 13.9 months, and median OS was 31 months in 30 patients receiving first-line treatment of six- month FOLFOX4 followed by UFT as maintaining treatment . A non-randomized small sample study conducted in department of medical oncology of Sun Yat-Sen University Cancer Center indicated that patients receiving first-line treatment of XELOX followed by capecitabine as maintaining therapy has significantly prolonged median TTP, comparing with the non-maintaining treatment patients,(14months vs. 9 month, respectively).

Above all, so far, there is no data to demonstrate that regular 4-6 month chemotherapy followed by maintaining treatment could prolong TTP and OS for advanced colorectal cancer. Capecitabine is effective for colorectal cancer, and was approved as palliative treatment for advanced colorectal cancer and adjuvant chemotherapy; in addition, with its relative less frequency of side effects and convenient oral administration, capecitabine as maintaining regimen could be prone to be accepted by patients. Therefore, our study is designed to investigate that capecitabine as maintaining treatment after first-line palliative chemotherapy could improve TTP and OS for patients with advanced colorectal cancer through a perspective randomized clinical study.

Patients with metastatic colorectal cancer who achieved objective response or stable disease after 4-6 months first-line chemotherapy were randomly assigned to one of two groups, to receive either capecitabine (2000 mg/m2 per day on days 1-14,Q3W) as maintenance therapy or observation. The treatment will continue until disease progression or unacceptable toxicity.

Inclusion Criteria:

• age older than 18 years
• Eastern Cooperative Oncology Group performance status (ECOG PS) 0-1
• histologically confirmed colorectal cancer with inoperable locally advanced or recurrent and/or metastatic disease, not amenable to curative therapy.
• Life expectancy of at least 3 months
• Hematologic, Biochemical and Organ Function 14. Neutrophil count < 1.5 × 109/L, or platelet count < 100 × 109/L. 15. Serum bilirubin > 1.5 × upper limit of normal (ULN); or, AST or ALT > 2.5 × ULN (or > 5 × ULN in patients with liver metastases); or, alkaline phosphatase > 2.5 × ULN (or > 5 × ULN in patients with liver metastases, or > 10 × ULN in patients with bone but no liver metastases); or albumin < 25 g/L
• Patients who achieved objective response or stable disease after 16-24 weeks first line chemotherapy
• Signed informed consent

Exclusion Criteria:

• Known hypersensitivity to capecitabine
• History or clinical evidence of brain metastases
• No previous chemotherapy for metastatic disease
• Positive serum pregnancy test in women of childbearing potential
• Subjects with reproductive potential not willing to use an effective method of contraception
• Received any investigational drug treatment within 4 weeks of start of study treatment
• other prior malignancies in the past 5 years
• unresolved bowel obstruction or malabsorption syndrome