Circulating Biochemical Markers of Gastro-Entero-Pancreatic (GEP) Neuroendocrine Neoplasms(NENs)

Neuroendocrine neoplasms (NENs) are a heterogeneous group of neoplasms which represent a true challenge for clinicians. Their incidence and prevalence have been increasing over the past years partly due to increased awareness and improvements in instrumental diagnostic techniques so that a growing number of clinicians are facing this disease. Management of NEN represents a clinical challenge because of its late presentation, scarcity of standardized guidelines, and limitations in imaging modalities and biomarkers to guide management. The beginning of the diagnostic process of NENs is often based on the measurement of circulating markers, before planning expensive and invasive diagnostic tests; however up to 60–80% of NENs are metastatic at diagnosis, which highlights the frequent failure to identify symptoms or to establish a biochemical diagnosis. Classical available markers, which can be divided into general and specific biomarkers, often lack sensitivity and/or specificity and need to be interpreted in the diagnostic process. Therefore, it is very important to know the advantages and limitations of these diagnostic tools. On the other hand, new biomarkers are emerging in the scenario of molecular diagnostics. This chapter aims to review the different characteristics of the available biomarkers, exposing the strengths and limitations of each, for their best clinical use.