PET/CT Scan as a Tool to Rationalize the Treatment of Patients With Advanced ColoRectal Cancer Undergoing First-line Medical Treatment

Inclusion Criteria: * Diagnosis histologically confirmed colorectal carcinoma * stage IV disease * patients eligible for standard first-line treatment medical therapy (chemotherapy, and when indicated in association with EGFR inhibitor and/or antiangiogenic) for advanced disease, at diagnosis or after primary surgery. * At least one target or non-target lesion according to RECIST revised version 1.1. * Age \> or = 18 years . * ECOG PS 0-2. * Life expectancy \> 3 months. * Signed informed consent. Exclusion Criteria: * Uncontrolled diabetes (glucose \> 200 mg/dl * Any other malignancies within 5 years (except for adequately treated carcinoma in situ of the cervix or basal or squamous cell skin cancer or surgically resected prostate cancer with normal PSA). * Pregnant or lactating females. * Previous medical therapy for metastatic disease (prior surgery, radiation therapy are permitted, as well as adjuvant medical therapy completed at least 6 months prior to study entry). * Any poorly controlled illness (including active infections, significant hepatic, renal, metabolic or cardiac disease, myocardial infarction within previous 12 months) that may, according to physician's judgement, interfere with the patient's ability to undergo chemotherapy and/or the examinations within the study protocol * Inability to provide informed consent.