The clinical implications and biologic relevance of neurofilament expression in gastroenteropancreatic neuroendocrine neoplasms.

BACKGROUND: Although gastroenteropancreatic neuroendocrine neoplasms (GEP-NENs) exhibit widely divergent behavior, limited biologic information (apart from Ki-67) is available to characterize malignancy. Therefore, the identification of alternative biomarkers is a key unmet need. Given the role of internexin alpha (INA) in neuronal development, the authors assessed its function in neuroendocrine cell systems and the clinical implications of its expression as a GEP-NEN biomarker.
METHODS: Functional assays were undertaken to investigate the mechanistic role of INA in the pancreatic BON cell line. Expression levels of INA were investigated in 50 pancreatic NENs (43 primaries, 7 metastases), 43 small intestinal NENs (25 primaries, 18 metastases), normal pancreas (n = 10), small intestinal mucosa (n = 16), normal enterochromaffin (EC) cells (n = 9), mouse xenografts (n = 4) and NEN cell lines (n = 6) using quantitative polymerase chain reaction, Western blot, and immunostaining analyses.
RESULTS: In BON cells, decreased levels of INA messenger RNA and protein were associated with the inhibition of both proliferation and mitogen-activated protein kinase (MAPK) signaling. INA was not expressed in normal neuroendocrine cells but was overexpressed (from 2-fold to 42-fold) in NEN cell lines and murine xenografts. In pancreatic NENs, INA was overexpressed compared with pancreatic adenocarcinomas and normal pancreas (27-fold [P = .0001], and 9-fold [P = .02], respectively). INA transcripts were correlated positively with Ki-67 (correlation coefficient [r] = 0.5; P < .0001) and chromogranin A (r = 0.59; P < .0001). INA distinguished between primary tumors and metastases (P = .02), and its expression was correlated with tumor size, infiltration, and grade (P < .05).
CONCLUSIONS: INA is a novel NEN biomarker, and its expression was associated with MAPK signaling and proliferation. In clinical samples, elevated INA was correlated with Ki-67 and identified malignancy. INA may provide additional biologic information relevant to delineation of both pancreatic NEN tumor phenotypes and clinical behavior.