Panitumumab and RAS, Diagnostically-useful Gene Mutation for mCRC

Inclusion Criteria: 1. Investigator and subinvestigator judge a candidate is understand clinical trial and comply this protocol. Investigator is those who participate in conducting a study and oversight the study duties at a site. 2. Patients who have given written consent to take part in the study after detailed explanation of the study prior to enrollment 3. Aged ≥20 to \<80 years at the time of informed consent 4. Patients with unresectable adenocarcinoma originating in the large intestine (excluding carcinoma of the appendix and anal canal cancer) 5. Patients with lesion(s) that can be evaluated. It is not essential to be evaluated the tumor according to the RECIST ver. 1.1. 6. Patients who have not received chemotherapy for colorectal cancer. Patients who experience relapse more than 24 weeks (168 days) after the final dose of perioperative adjuvant chemotherapy with fluoropyrimidine agents may be enrolled. Patients who have received perioperative adjuvant chemotherapy including oxaliplatin are excluded. 7. Patients classified as KRAS/NRAS wild-type by KRAS/NRAS testing. KRAS/NRAS test will be performed using the in vitro diagnostic listed in the National Health Insurance. Patients with no mutation in any of the codons shown below are considered wild type. It is not considered wild type if either of the codons are not evaluable or not tested. KRAS: EXON2 (codon 12, 13), EXON3 (codon 59, 61), EXON4 (codon 117, 146) NRAS：EXON2 (codon 12, 13), EXON3 (codon 59, 61), EXON4 (codon 117, 146) 8. Patients who satisfy the following criteria for the major organ function in tests performed within 14 days prior to enrollment * Neutrophil count ≥ 1.5×10\^3/µL * Platelet count ≥ 1.0×10\^4/µL * Hemoglobin ≥ 9.0 g/dL * Total bilirubin ≤ 2.0 mg/dL * AST ≤ 100 IU/L (≤ 200 IU/L if liver metastases are present) * ALT ≤ 100 IU/L (≤ 200 IU/L if liver metastases are present) * Serum creatinine ≤ 1.5 mg/dL * PT-INR \< 1.5 (\< 3.0 for patients treated with oral warfarin) * Satisfies at least one of these conditions 1. Urine protein (dip stick method) ≤ 1+ 2. UPC (urine protein creatinine) ratio ≤ 1.0 3. Urinary protein ≤ 1000 mg/ 24hours 9. ECOG performance status (PS) of 0 or 1 10. Life expectancy of ≥ 3 months (90 days) after enrollment Exclusion Criteria: 1. Radiotherapy received within 4 weeks (28 days) prior to enrollment. Treatments aimed at relieving pain for bone metastases are excluded. 2. Known brain metastasis or strongly suspected of brain metastasis 3. Synchronous cancers or metachronous cancers with a disease-free period of ≤ 5 years (excluding colorectal cancer) excluding mucosal cancers cured or be possibly cured by regional resection (esophageal, stomach, and cervical cancer, non-melanoma skin cancer, bladder cancer, etc.). 4. Body cavity fluid that requires treatment (pleural effusion, ascites, pericardial effusion, etc.) 5. Patients who do not want to use contraception to prevent pregnancy, and women who are pregnant or breast-feeding, or test positive for pregnancy 6. Nonhealing surgical wound (excluding implanted venous reservoirs) 7. Active hemorrhage requiring blood transfusion 8. Disease requiring systemic steroids for treatment (excluding topical steroids) 9. The patient who has placed colonic stent 10. Intestinal resection within 4 weeks prior to enrollment or colostomy within 2 weeks prior to enrollmentt 11. History or obvious and extensive CT findings of interstitial pulmonary disease (interstitial pneumonia, pulmonary fibrosis, etc.) 12. Patients with unstable angina, myocardial infarction, cerebral hemorrhage, arterial thromboembolism such as cerebral infarction, or have history of these desease less than 24 weeks (168 days) before registration (except for lacunar infarction asymptomatic) 13. Serious drug hypersensitivity 14. Local or systemic active infection requiring treatment, or fever indicating infection 15. NYHA class II or higher heart failure or serious heart disease 16. Intestinal paralysis, gastrointestinal obstruction, or uncontrollable diarrhoea (incapacitating symptoms despite adequate treatment) 17. Poorly controlled hypertension 18. Poorly controlled diabetes mellitus 19. Active hepatitis B 20. Known HIV infection 21. Peripheral neuropathy of ≥ Grade 2 by CTCAE (Japanese edition JCOG version 4.03) 22. Other patients judged by the investigator or subinvestigator to be ineligible for enrollment in the study (e.g. Patients who might agree to participate under compulsion).