Survival of patients with metastatic cancer has increased over the past two decades as a result of a progressive improvement of regional and systemic therapies. However, oncologists' estimates of patients' predicted overall survival in metastatic cancer are imprecise. The purpose of this book is to systematize the evidence regarding the prognostic factors of metastatic gastrointestinal tumors, separating the findings with the highest level of evidence among those available for each disease by selecting studies with the highest scientific evidence level.