Serotoninergic brain dysfunction in neuroendocrine tumor patients: A scoping review

Introduction: Neuroendocrine tumors (NETs) are rare and malignant neoplasms characterized by their potential to produce metabolically active substances with the capacity to bring about clinical syndromes. The clinical expression of serotonin-producing NETs is known as carcinoid syndrome (CS). The synthesis of serotonin in the brain is dependent on tryptophan availability. At the central level, serotonin is indispensable for mood, anxiety, and sleep regulation. In CS patients, around 60% of all tryptophan is reported to be consumed by tumor cells for the peripheral synthesis of serotonin, increasing the risk of a central deficiency and thus psychiatric disorders. Materials and methods: This manuscript reviews the existing literature about psychiatric disorders associated with NETs and addresses the safety of psychiatric drugs in these patients. A systematic search of the biomedical literature was performed using the following databases: PubMed, Embase, CINAHL (EBSCO), PsycInfo (OVID), and Cochrane CENTRAL (Wiley). The database search included articles published between January 1965 and February 2021. Relevant information were charted using a calibrated charting-form. Results: Twenty-two articles were included in the present review. The overall population size of the studies came to 3319 patients. All patients presented a confirmed diagnosis of NET. The information about the presence of CS was confirmed in 351 cases. The psychiatric symptoms reported included mood disturbances (including, depression and anxiety), psychoses, impulse control disorders and sleeping alterations. We also evaluated the presence of cognitive impairments in NET patients. Finally, we summarize the available data regarding the safety of psychiatric drugs in this setting. Conclusions: Psychiatric disorders among NET patients are poorly recognized, and therefore have received very little research attention. As a result, no standardized algorithm is presently available. Our findings support detailed psychiatric evaluation in NET patients, especially in those presenting CS and symptoms suggestive of psychiatric involvement. Not only do cognitive impairment and psychiatry symptoms negatively impact health-related quality of life in cancer patients, they can also reduce survival rates.