ObjectiveTo determine the association between neuroendocrine tumor (NET) biomarker levels and the extent of disease as assessed by⁶⁸Ga DOTATATE PET/CT imaging.DesignA retrospective analysis of a prospective database of patients with NETs.MethodsFasting plasma chromogranin A (CgA), neuron-specific enolase (NSE), gastrin, glucagon, vasoactive intestinal peptide (VIP) and pancreatic polypeptide (PP), and 24-h urinary 5-hydroxyindoleacetic acid (5-HIAA) levels were measured. Correlation between biomarkers and total⁶⁸Ga-DOTATATE-avid tumor volume (TV) was analyzed.ResultsThe analysis included 232 patients. In patients with pancreatic NETs (n = 112),⁶⁸Ga-DOTATATE TV correlated with CgA (r = 0.6,P = 0.001, Spearman). In patients with multiple endocrine neoplasia type 1 (n = 39),⁶⁸Ga-DOTATATE TV correlated with glucagon (r = 0.5,P = 0.01) and PP levels (r = 0.5,P = 0.049). In patients with von Hippel–Lindau (n = 24), plasma VIP (r = 0.5,P = 0.02) and PP levels (r = 0.7,P < 0.001) correlated with⁶⁸Ga-DOTATATE TV. In patients with small intestine NET (SINET,n = 74),⁶⁸Ga-DOTATATE TV correlated with CgA (r = 0.5,P = 0.02) and 5-HIAA levels (r = 0.7,P < 0.001), with 5-HIAA ≥8.1 mg/24 h associated with metastatic disease with high positive (81.8%) and negative (85.7%) predictive values (P = 0.001).⁶⁸Ga-DOTATATE TV in patients with NET of unknown primary (n = 16) and those with NET of other primary location (n = 30) correlated with 5-HIAA levels (r = 0.8,P = 0.002 andr = 0.7,P = 0.02 respectively).ConclusionsOur data supports the use of specific NET biomarkers based on the site of the primary NET and the presence of hereditary syndrome-associated NET. High urinary 5-HIAA levels indicate the presence of metastatic disease in patients with SINET.