[529] Comparison between the Conventional and Phospho-Histone H3 (PHH3) Immunohistochemistry-Assisted Mitotic Count in Different Subtypes of Melanomas

Vladimir O Osipov, Thilanie Purdy, Leanne C Giles. Labtests, Auckland, New Zealand

Background: The mitotic count in melanocytic lesions is an important diagnostic and prognostic factor. It can be difficult to reliably identify mitotic figures in H&E stained sections. We investigated whether mitotic count using Phospho-Histone H3 (PHH3) immunohistochemistry would produce less inter-observer variability in comparison with H&E stained sections. Another aim of the study was to see whether PHH3 would be helpful in the diagnosis of nevoid and desmoplastic melanomas.
Design: Formalin-fixed, paraffin-embedded tissue of 110 conventional invasive, 9 nevoid and 8 desmoplastic melanomas were used in this study. Sections from these 127 tumours were stained with H&E and PHH3. Mitotic count per 1 mm2 was performed in both H&E and PHH3-stained sections independently by two pathologists and by two histotechnologists. Intradermal nevi were used as a negative control on each slide. Data were assessed by the Bland-Altman (BA) analysis.
Results: Combined mean mitotic count for all cases on PHH3 stained sections was three times higher than on H&E for all of the participants as a group. Comparison of the mitotic count on H&E between pathologists and histotechnologists showed poor reproducibility with BA analysis showing mean difference -7.25 [CI -28.25-14.37]). In contrast, comparison of mitotic counts between pathologists and histotechnologists on PHH3 stain resulted in BA mean difference -0.34 [CI -2.75-2.11]), indicating good reproducibility between the participants. Mitoses were easily identified in PHH3 stain in nevoid and desmoplastic melanomas. Of 127 nevi only 18 showed 1-2 mitoses per slide in PHH3 stained sections.
Conclusions: PHH3 facilitates the mitotic count. Number of mitoses in melanomas assessed by PHH-3 staining is three times higher than by H&E. PHH3 allows for more reproducible mitotic counts than by H&E. PHH3 confirms mitotic inertness of the intradermal nevi, while clearly highlighting deep dermal mitoses in nevoid and desmoplastic melanomas.
Category: Dermatopathology

Wednesday, March 21, 2012 1:00 PM

Poster Session VI # 123, Wednesday Afternoon


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