In midgut NETs serotonin production is most prominent. Patients with NETs producing excessive serotonin can develop carcinoid syndrome. Serotonin is a product of the 'tryptophan pathway'. Serotonin is metabolized in 5-hydroxyindolacetic acid (5-HIAA) and then excreted with urine. 5-HIAA in 24-hour urine collection is one of the parameters used for follow up in patients with a serotonin-producing neuroendocrine tumor. This measurement has some disadvantages; it could be stressful, the collection is not always precisely, furthermore the collection could be problematic, for example in patients with diarrhea.~Since October 2013 it is possible, because of a better measurement sensitivity, to measure reliably 5-HIAA in platelet rich plasma (PRP) by isotope-dilution massa-spectrometer (LCMS-MS). Recent publications show that 5-HIAA measured in PRP could have an additive value in diagnosis and follow up of patients with serotonin-producing NET.~Objective:~The primary objective is to measure the correlation between 5-HIAA in PRP and 5-HIAA in 24-hours urine collection in adult patients with a serotonin-producing neuro-endocrine tumor.~Secondary objective is to determine if increase or decrease of 5-HIAA in plasma is associated with disease progression.~Study design:~This is an observational laboratory study. Plasma and urine of included patients and collected in standard health care, are selected and the 5-HIAA's are measured with LCMS-MS. Also age, sex, diagnosis and clinical course of the patients will be collected from the medical record.~Study population:~In this study the investigators will use blood and urine of 60 patients with serotonin-producing neuro-endocrine tumors.~Main study parameters/endpoints:~The main endpoint of this study is the correlation between 5-HIAA in PRP and 5-HIAA in 24-hour urine collection. Secondary endpoint is the correlation between 5-HIAA in PRP and course of the disease, determined by CT-scan (if applicable).
The objective of this observational laboratory study is to measure the correlation between 5-hydroxyindolacetic acid (5-HIAA) in platelet rich plasma and 5-HIAA in 24-hours urine collection in adult patients with a serotonin-producing neuro-endocrine tumor. Plasma and urine of included patients are collected and 5-HIAA values are measured with LCMS-MS and analysed.