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M. Angi, B. Damato, A. F. G. Taktak, S. E. Coupland; Immunohistochemical Assesment of Mitotic Index in Uveal Melanoma. Invest. Ophthalmol. Vis. Sci. 2009;50(13):6180.
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© ARVO (1962-2015); The Authors (2016-present)
The mitotic index (MI) of uveal melanomas correlates with the risk of metastatic death, but with haematoxylin and eosin(H&E)-stained sections it is difficult to identify mitotic figures (MF) reliably. We investigated whether this measurement could be enhanced by immunohistochemistry, using the mitosis-specific marker Phospoho-Histone H3 Ser10 (PHH3).
We assessed 130 choroidal melanomas, which had been treated by enucleation (115) or trans-scleral local resection (15) at our centre between 2006 and 2008. Formalin-fixed, paraffin-embedded, 4µ-thick sections were stained with H&E as well as the anti-PHH3 antibody (Ser10, Epitomics, Burlingame, CA) respectively. MI was defined as the sum of MF counted in 40 high power fields (HPF). With PHH3-stained sections, MI was determined independently by an experienced pathologist (SEC) and by a trainee ophthalmologist (MA). Comparisons were assessed statistically using the Kolmogorov-Smirnov (Z) test and by analyzing Pearson’s correlation coefficient (R).
The tumors had a median diameter of 16.4 mm (range, 7.6-22.8) and a median height of 8.3 mm (range, 1.2 - 18.1). Epithelioid cells and closed connective tissue loops occurred in 66.2% and 53.1% respectively. Cytogenetic studies were performed in 112 cases and showed monosomy 3 in 50.9%. The MIs determined by SEC with H&E and PHH3 had median values of 4/40 HPF and 8/40 HPF respectively (Z, p = 0.76; R, 0.64), indicating poor repeatability with these two methods. The median MIs determined by SEC & MA using PHH3 were 8/40 HPF and 9/40 HPF respectively (Z, p<0.001; R, 0.996), indicating good repeatability between examiners.
MF were more easily (and quickly) identified with the aid of immunohistochemistry using PHH3. This resulted in higher mitotic counts than obtained with H&E sections. With PHH3, MIs determined by a trainee ophthalmologist were virtually the same as those obtained by an experienced pathologist. PHH3 is now routinely used in our centre and new prognostic thresholds for uveal melanoma will be defined in further studies.
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