Phosphorylated Histone H3 (PHH3) Is a Superior Proliferation Marker for Prognosis of Pancreatic Neuroendocrine Tumors

Background: The staging of pancreatic neuroendocrine tumors (PNETs) is continuously evolving. Mitotic count, as measured by hematoxylin and eosin (H&E) or Ki67 labeling index (Ki67LI), is the best predictor of disease biology. However, both of these methods have several limitations. Phosphorylated histone H3 (PHH3), a novel mitotic marker, is potentially more accurate and easier to evaluate. This study aimed to evaluate the prognostic impact of PHH3 on patients with PNETs. Methods: Clinicopathologic data and paraffin-embedded tissue were evaluated for 100 of the 247 PNET patients whose tumors were resected between 1998 and 2010. Mitotic counts were analyzed on H&E-, Ki67-, and PHH3-stained slides by two independent pathologists. Kaplan–Meier curves, log-rank tests, Cox regression models, and time-dependent receiver operative characteristics (ROC) curves were used to evaluate the prognostic power of these markers. An internal data cross-validation was performed to select the best cutoff. Results: Of the 100 PNET patients resected, 53 were men. The median age of the patients was 59 years (range 19–96 years). The median follow-up period was 68 months (range 3–186 months). The median time for evaluation of an H&E- or PHH3-stained slide was 3 min, relative to 15 min for Ki67. The findings showed H&E, Ki67, and PHH3 all to be excellent predictors of disease-specific survival (DSS). However, PHH3 was superior to H&E and Ki67 in predicting both disease-free survival (DFS) (p = 0.006) and DSS (p = 0.001). Evaluation of the PHH3 mitotic count showed 7 mitoses per 10 high-power fields (HPFs) to be the optimal cutoff for differentiating between low- and high-risk PNET patients. Conclusions: PHH3 is a better predictor of both DFS and DSS than H&E or Ki67 in PNET. In addition, PHH3 appears to be both easier to interpret and more accurate when compared to current prognostic markers.