Chapter 4 - Immunotherapy in gastrointestinal cancers: Spotlight on the pivotal role of currently available biomarkers

Gastrointestinal (GI) cancers represent a major health burden, especially due to their elevated incidence and poor prognosis. In the past decade, immunotherapy, currently driven by the application of monoclonal antibodies targeting immune checkpoints, has revolutionized the therapeutic landscape of many solid tumors, including GI cancers. Unfortunately, only a subset of patients responds to immune checkpoint inhibitors, and the development of secondary resistance is increasing. In this chapter, we will outline the most relevant biomarkers for gastroesophageal, bowel, anal, and biliopancreatic cancers and gastroenteropancreatic neuroendocrine neoplasms, and we will discuss their prognostic and predictive value and their use in clinical practice.