The objective of the study is to create a common and unique platform for the acquisition of biological samples and, subsequently, the possible identification of predictive and prognostic biomarkers for young adults with gastrointestinal and neuroendocrine cancers.The definition "adolescent and young adults (AYA)" covers a broad group of patients ranging from the upper limit of the paediatric competence to the youngest patients usually considered and treated as adults. However, a well-defined and universally accepted age range is still not established. Young adults with cancer have distinct epidemiological, biological, and clinical characteristics, as well as special medical and psychosocial needs that are often unmet. In consideration of their poor representation in clinical studies, as well as the rarer, albeit increasing, frequency at an epidemiological level, knowledge of the risk factors associated with cancers in young adults is very poor. It is therefore of fundamental importance to focus attention on this specific cohort of patients, in order to describe in ever more detail any specific biomolecular aspects, and make full use of the pharmacological resources currently available.