Fine-needle aspiration–based grading of pancreatic neuroendocrine neoplasms using Ki-67: is accurate WHO grading possible on cytologic material?

The World Health Organization (WHO) has provided grading guidelines for pancreatic neuroendocrine neoplasms (PanNENs) based on mitotic count and Ki-67 proliferation index. Due to the desire to provide earlier tumor grading for clinical management decisions, some groups have proposed grading PanNENs at the time of fine needle aspiration (FNA) using Ki-67 proliferation rates. While a Ki-67 can be performed on FNA cell blocks, there are potential...