Feasibility study of combination therapy with S-1 plus irinotecan in patients with EGFR positive KRAS mutation type unresectable colorectal cancer, who had previously received on irinotecan, oxaliplatin and fluoropyrimidine, bevacizumab

INTERVENTION: S‐1/irinotecan combination therapy Irinotecan 100 mg/m2(day1,15), S‐1 80‐120mg/day, PO from day1 to day 14 of each 28 day cycle. CONDITION: Colorectal cancer PRIMARY OUTCOME: Progression free survival(PFS) SECONDARY OUTCOME: Overall response rate ; Overall survival ; Disease control rate (CR+PR+SD); Safety INCLUSION CRITERIA: 1) Patients with histologically proven colorectal cancer and clinically proven unresectable advanced/recurrent colorectal cancer 2) KRAS mutation type 3) Age 20 years<= 80 4) Patients who had previously received on irinotecan, oxaliplatin and fluoropyrimidine,bevacizumab 5) ECOG performance status 0‐1 6) Presence of measurable lesion judged by enhanced CT (according to the RECIST 1.1) 7) Patiens have enough organ function based on blood test within 28day before registration. 1.WBC>=3,000/mm3<=12,000/mm3 2.Neurtophils>=1,500/mm3 3. Platelets>=100,000/mm3 4. Hemoglobin>=9.0g/dl 5. Total bilirubin<=2.0mg/dl 6.AST<=100IU/L(ALT<=200IU/L with liver metastases) 7.ALT<=100IU/L(ALT<=200IU/L with liver metastases) 8. Creatinine<=1.2mg/dl 9. creatinine clearance>=50ml/min 8)Be able to take oral drugs 9)Life expectancy at least 3 months 10)Written informed consent