Study to Evaluate the Efficacy and Safety of FOLFIRI-AD in Patients With Metastatic Colorectal Cancer UGT1A Genotype 1

Inclusion Criteria: * Histologically confirmed metastatic colorectal adenocarcinoma not curable surgically. * Not received prior systemic therapy for metastatic colorectal cancer. It allows receiving neoadjuvant or adjuvant chemotherapy (without irinotecan) as a treatment of the primary tumor at least six months before inclusion. All toxicities secondary to previous treatment should have been resolved before inclusion. The progression of disease (metastatic disease) should be confirmed radiologically after adjuvant treatment. * Genotype of the gene UGT1A1 \* 1 / \* 1 or \* 1 / \* 28 * Age\> or = 18 and \<75 years. * ECOG 0-1. * Measurable disease according to RECIST version 1.1 * Life expectancy\> or equal to 3 months. * Informed consent, dated and signed. * Adequate bone marrow function as: Hemoglobin ≥ 9.0 g / dl (patients with hemoglobin \<9 g / dl may be transfused before inclusion in the study) Platelet count ≥ 100 x 109 / L Absolute neutrophil count (ANC) ≥ 1.5x 109 / L - Adequate liver function as: Serum bilirubin ≤ 1.5 x upper limit of normal (ULN) Alanine aminotransferase (ALT) and aspartate aminotransferase (AST) ≤ 2.5 x ULN in the absence of liver metastases and ALT and AST ≤ 5 × ULN in the presence of liver metastases Alkaline phosphatase ≤ 2.5 x ULN or ≤ 5 x ULN in the presence of liver metastases or ≤ 10 x ULN in the presence of bone metastases \- Adequate renal function with creatinine levels \<1.5 mg / dL. BUN\> 50 ml / min Exclusion Criteria: * Genotype of the gene UGT1A1 \* 28 / \* 28 (Gilbert's syndrome) * Patients who are pregnant or breast-feeding * Concomitant treatment with other antineoplastic therapy other than specified. * Patients with active infectious processes and patients with immunosuppressive therapy, or chronic anticoagulant therapy. * History of malignancy in the last five years except basal cell carcinoma of the skin or carcinoma in situ of the cervix treated properly. * Patients with positive serology for HIV previously known, chronic diarrhea, inflammatory bowel disease or malabsorption syndrome or tumor obstruction unresolved. * Clinically significant cardiovascular disease: cerebrovascular accident / stroke (≤ 6 months before inclusion in the trial), myocardial infarction (≤ 6 months before inclusion in the trial), unstable angina, uncontrolled hypertension, congestive heart failure grade II or higher NYHA or serious cardiac arrhythmia. * Patients with significant neurological or psychiatric disorders, including dementia or poorly controlled epilepsy. * Patients with any contraindications specified in the Summary of study drug.