This phase II trial on the assumption that S-1 combined with Leucovorin may have better efficacy and safety than simplified 5-FU/LV infusion therapy in elderly patients with advanced colorectal cancer.

This is a randomized phase Ⅱ study, in which S-1 is used in combination with leucovorin in elderly patients with advanced colorectal cancer as first-line treatment,comparing with sLV5FU2 therapy. The aim of this study is to determine the efficacy and safety of S-1/LV in elderly patients in the first-line setting. The other secondary endpoints are progression free survival,overall survival, and quality of life are also evaluated.

Inclusion Criteria:

• Signed written informed consent
• Oral medication is acceptable
• Histologically confirmed colorectal carcinoma
• Male or female ≥ 65 years of age
• No prior chemotherapy,radiotherapy,target therapy and immunotherapy, except adjuvant chemotherapy with an interval of ≥ 180 days)
• Presence of at least one target lesion measurable by CT scan or MRI,within 15 days prior to trial
• The lab values within 2 weeks prior to trial should meet:

PLT ≥7.5*10^4/mm3 ANC≥2000/mm3 HB≥100g/L Total bilirubin < upper limit of normal level ALT/AST/ALP < 2.5 x UNL (<5 x UNL for patients with liver or bone metastasis) Serum creatinine < UNL

• Performance status (ECOG) 0~1
• Life expectation longer than 90 days

Exclusion Criteria:

• Allergy to S-1,fluorouracil or leucovorin
• Any investigational agent(s) within 4 weeks prior to entry
• Previous or currently exposure to certain drugs which are proved to have influence on blood drug concentration
• Active infection
• Severe organ failures or diseases, including: intestinal obstruction, pulmonary fibrosis, uncontrolled diabetes mellitus,clinically relevant coronary disease, cardiovascular disorder or myocardial infarction,renal or liver failure, severe psychiatric illness,cerebral vascular disease and sever GI ulcer which need blood infusion.
• Uncontrolled hydrothorax,ascites and hydropericardium
• Multiple bone metastatic lesions
• Brain metastases
• Chronic diarrhea or digestive disfunction
• Previous malignancy (except colorectal cancer, history of basal cell carcinoma of skin or pre-invasive carcinoma of the cervix with adequate treatment)
• Strong willingness to receive surgery or highly potential to have intestinal obstruction which may need surgery intervention
• Other conditions that primary investigate or investigator consider to be unsuitable for the trial