Phosphohistone H3 and Ki-67 Labeling Indices in Cytologic Specimens from Well-Differentiated Neuroendocrine Tumors of the Gastrointestinal Tract and Pancreas: A Comparative Analysis Using Automated Image CytometryFung A.D.a · Cohen C.a · Kavuri S.b · Lawson D.a · Gao X.a · Reid M.D.a
aDepartment of Pathology, Emory University School of Medicine, Atlanta, Ga., and bDepartment of Pathology, Georgia Health Sciences University, Augusta, Ga., USA
Background: Ki-67 proliferation index was recently incorporated in the grading of neuroendocrine neoplasms (NENs) of the gastrointestinal tract (GIT) and pancreas. These are now divided into well-differentiated neuroendocrine tumors (WDNETs, grades 1 and 2) and poorly differentiated neuroendocrine carcinomas (grade 3). While Ki-67 is an established proliferation marker in NENs, phosphohistone H3 (PHH3), a newer marker of mitotic activity, is not. Methods: We determined Ki-67 and PHH3 indices on cytologic samples from WDNETs of the GIT and pancreas using an automated cellular imaging system (ACIS®). Results: There was a strong correlation between Ki-67 and PHH3 indices generated by ACIS on cytologic samples. However, in some cases the two stains caused conflicting grades within the same tumor. Conclusion: Both antibodies stain cells in different phases of the cell cycle which may cause discordant grades, thus affecting patient management and prognostication. Ki-67 staining is stronger than PHH3, making ‘hot spots' easier to identify on ACIS. Ki-67 is more ideal than PHH3 for staining NENs, especially in tumors with borderline grades. Because PHH3 generates lower mitotic indices it should not be used as a proliferation marker in NENs until its expression has been further characterized.