18F-FDG Uptake in Well-Differentiated Neuroendocrine Tumors Correlates with Both Ki-67 and VHL Pathway Inactivation

18F-FDG-PET scan positivity correlates with poor prognosis in neuroendocrine neoplasms (NEN). Glucose transporter 1 (GLUT1) and carbonic anhydrase 9 (CA9) are markers of aggressiveness in tumors. Together with von Hippel-Lindau protein (pVHL), they are involved in tumor cell metabolism via the hypoxia-inducible factor signaling pathway. The aim of this study was to compare, in a series of well-differentiated neuroendocrine tumors (NET), the 18F-FDG uptake and expression of the proliferation markers Ki-67, GLUT1, CA9, and pVHL.

This retrospective study included 27 patients with well-differentiated NET. 18F-FDG-PET images were evaluated by the maximum standardized uptake value (SUVmax). GLUT1, CA9, and pVHL were analyzed by immunohistochemistry.

The NET were of pancreatic (n = 19), midgut (n = 4), duodenal (n = 1), esophageal (n = 1), rectal (n = 1), and pulmonary (n = 1) origin. Eight, 11, and 8 tumors were grade 1, 2, and 3, respectively. The mean/median Ki-67 index was 15/10% (1-60). The mean/median SUVmax was 6.2/5.2 (1.4-18.7). SUVmax correlated with greater tumor size (p = 0.03), higher expression of Ki-67 (p = 0.04), and lower expression of pVHL (p = 0.008). In the group of 16 NET with a low proliferative index (Ki-67 index <10%), 5/6 (83%) of the tumors with a high SUVmax had decreased pVHL expression (p = 0.0013).

This study confirms that 18F-FDG-PET uptake correlates with both tumor size and proliferation in well-differentiated NET, and it highlights a subset of low-grade but 18F-FDG-PET-positive NET related to sporadic inactivation of the VHL pathway.