Functioning neuroendocrine tumors (NET): Minimum requirements for a NET specialist

Functioning neuroendocrine tumors (f-NETs) represent a minority of all NETs, however their management is challenging due to the impact on patients' survival and quality of life. In addition to f-NETs, paraneoplastic syndromes (PNS) are due to substances that are not related to the primary anatomical site, they can develop in different phases of NETs evolution, and might complicate the patient's clinical course. Dedicated guidelines are still scanty. We aim to review available literature on f-NETs to propose a useful tool for clinicians in order to improve the diagnostic process and the management.

Narrative review focused on f-NETs.

The most common f-NETs include insulinomas, gastrinomas and carcinoid syndrome (CS)- associated NETs. Symptoms related to hormone production may overlap with other common endocrine and gastrointestinal disorders, highlighting the pivotal role of multidisciplinary management. Somatostatin analogs (SSAs) represent the gold standard first-line treatment of most f-NETs, often followed by or combined with other treatments (surgery, liver-directed therapies, targeted therapies, peptide receptor radionuclide therapy). Paraneoplastic syndromes can develop in different phases of NET evolution and might complicate the patient's clinical course and response to therapy.

The management of hormonal syndromes is challenging and must be based on the multidisciplinary approach. Herein, we pointed out the minimal requirements for a NET specialist in the diagnosis and treatment of f-NETs. Efforts should be made to improve the awareness of functioning forms, to understand their pathogenesis and to improve their management.