Objective: The pathogenesis of pancreatic neuroendocrine tumors (PNETs) is still unclear. We propose Frabin as a new molecular alteration in PNETs. Frabin is a guanine nucleotide exchange factor playing a role in mediating actin cytoskeleton changes during cell migration, morphogenesis, polarization, and division.
Methods: Patients with PNETs of different grades were assessed for Frabin expression using immunohistochemistry and tissue microarray. The tissue microarray included 12 grade 1 and 3 grade 2 PNETs and 14 grade 3 pancreatic neuroendocrine carcinomas (PECAs). Frabin immunostain was scored with Allred system. Statistical analysis used SAS and R software. Immunohistochemistry scores were correlated with tumor grade and stage. The Spearman correlation coefficient was calculated with P values.
Results: Pancreatic neuroendocrine tumors were graded according to the World Health Organization 2017 guidelines. Frabin was expressed by 24 (82.7%) of the PNET/PECA studied. Only 5 (17.2%) of the 29 PNETs/PECA evaluated were Frabin negative. Frabin expression was cytoplasmic in all cases. We found a significant positive correlation (ρ = 0.47) between Frabin immunohistochemistry score and tumor grade (P = 0.01). No correlation was found between Frabin expression and tumor stage (P = 0.91).
Conclusions: We report Frabin overexpression as a novel molecular alteration occurring in PNETs/PECAs.