Grading Pancreatic Neuroendocrine Tumors via Endoscopic Ultrasound-Guided Fine Needle Aspiration: A Multi-Institutional Study

Abstract

Introduction: World Health Organization (WHO) grading system is prognostic in pancreatic neuroendocrine tumors (PanNETs). Concordance between WHO-grade on cytology (c-grade) of endoscopic ultrasound-guided fine needle aspiration (EUS-FNA) and histopathological analysis (h-grade) of surgical specimen is reported between 60% and 80%. Factors associated with concordance and trends of utilization of EUS-FNA remain poorly understood. Methods: A multicenter retrospective study was performed on patients undergoing resection for PanNETs at four high-volume centers. Patients with functional or syndrome-associated tumors, and those receiving neoadjuvant therapy were excluded. Factors associated with concordance and trends of utilization of EUS-FNA were assessed. Results: Of 1,329 patients, 682 (51.1%) underwent EUS-FNA; 567(83.1%) were diagnostic of PanNETs and WHO-grade was reported for 293 (51.7%) patients. The concordance between c-grade and h-grade was 78.2% with moderate inter-rater agreement (Kc=0.48,p<0.001). Significantly higher rates of concordance were observed in patients with smaller tumors (<2 vs. ≥2 cm, 88.9% vs. 72.7%,p=0.001). The highest concordance of 97.9% was observed in patients with small tumors undergoing assessment between 2015-2019 with near perfect inter-rater agreement (Kc=0.88, p<0.001) An increase in utilization of EUS-FNA (46.7% to 62.1%) was observed over the last 2 decades (p<0.001). EUS-FNA was more frequently diagnostic of PanNETs (p<0.001), and WHO-grade was more frequently reported (<0.001). Concordance between c-grade and h-grade did not change significantly (p=0.056). Conclusion: Recently, a trend towards increasing utilization and improved diagnostic accuracy of EUS-FNA has been observed in PanNETs. Concordance between c-grade and h-grade is associated with tumor size with strong agreement when assessing PanNETs >2cm in size.