The study consists of 40 patients with advanced colorectal cancer patients. All patients will be studied with 18F-FDG PET/CT combined with diagnostic contrast enhanced abdominal CT before the start of chemotherapy and re-evaluated 4-5 weeks after the initiation of therapy. Effect of this metabolic and anatomic change in therapy are evaluated and correlated to survival, morbidity, and treatment -related costs. Histopathologic confirmation of response is evaluated whenever possible. The data will be collected between 2008 and 2012.