Grading by the Ki-67 Labeling Index of Endoscopic Ultrasound-Guided Fine Needle Aspiration Biopsy Specimens of Pancreatic Neuroendocrine Tumors Can Be Underestimated

Objectives There is an increasing need for grading with small endoscopic ultrasound-guided fine needle aspiration biopsy (EUS-FNAB) specimens for the proper diagnosis and therapy selection of patients with unresectable pancreatic neuroendocrine tumors (PanNET). However, our understanding of EUS-FNAB specimen grading is limited compared with surgically resected specimens. Methods We retrospectively determined Ki-67 labeling index (LI) of 33 matched EUS-FNAB and surgically resected PanNETs with digital image analyzer. Pairwise grades between the matched biopsy and surgically resected PanNET specimens were compared. Results The mean Ki-67 LI was higher in surgically resected PanNET specimens (5.5%) than in biopsy specimens (3.2%; P = 0.022). There was moderate agreement between the Ki-67 LI grades when individually evaluated matched biopsy and resected specimen pairs were compared ( value = 0.62; P < 0.0001). However, discordance was noted in 6 cases (18%), and all of them were either grade 2 or 3 in resected PanNETs. Conclusions Although Ki-67 LI grading of EUS-FNAB specimens may be concordant with that of matched surgically resected specimens in a large proportion of the PanNET cases, Ki-67 LI grading of EUS-FNAB specimens should be carefully applied in clinical practice because of the possibility of grading underestimation with grade 2 to 3 PanNET cases.