Proposal for a Simplified Mib1 Assessment in Pancreatic Endocrine Tumors
Annika Blank, Laurie Boos, Inti Zlobec, Paul Komminoth, Aurel Perren, Anja M Schmitt. University of Bern, Bern, Switzerland; Technical University Munich, Munich, Germany; City Hospital Triemli, Zurich, Switzerland
Background: The prediction of biological behavior in pancreatic endocrine tumors (PET) is challenging in the absence of metastases. The WHO 2010 classification requires grading by assessment of the Mib1 index. This requires counting of 2000 cells in a hot-spot. As this procedure is not easily performed in clinical routine the aim of the present study was to test a simplified assessment of the proliferation index in PET.
Design: In a first step Mib1 staining was examined by counting the number of positive tumor cells per HPF (0.2mm2) in TMA punches of 133 primary sporadic PET. In a second step using whole slide sections of the same cohort Mib1 positive tumor cells were counted in 1mm2 in the centre and in the periphery of the tumor.
ROC analysis was performed to obtain the optimal cut-off for the number of tumor cells positive for Mib1 regarding risk stratification. Results were correlated with Mib1 proliferation index (2%) as well as with survival data.
Results: Overall the number of Mib1 positive tumor cells correlated significantly with the Mib1 proliferation index. ROC analysis showed a cut-off of ≤7 tumor cells/0.2mm2 staining with Mib1 for an optimal risk stratification on the TMA in the present cohort.
On whole slide sections, in the center of the tumor the mean value of positive tumor cells was the best predictor for disease-free survival, whereas in the periphery of the tumor the maximum value of positive tumor cells was the best predictor for disease-free survivial. No such difference could be detected regarding disease-specific survival.
Conclusions: In the present study we demonstrate a simplified method to assess the proliferation of PET by counting the number of tumor cells staining with Mib1. This method could substitute for the presently recommended proliferation index.
Tuesday, March 20, 2012 1:00 PM
Poster Session IV # 41, Tuesday Afternoon