The mitosis-specific antibody anti-phosphohistone-H3 (PHH3) facilitates rapid reliable grading of meningiomas according to WHO 2000 criteria

Mitotic figure (MF) counting is the most objective criterion for grading of meningiomas according to the 2000 World Health Organization (WHO) classification. However, the search for the area(s) of highest mitotic activity is tedious, and there is high interobserver variability in differentiating MF from apoptotic cells. We tested the utility of the mitosis-specific marker phosphohistone-H3 (PHH3) to enhance rapid recognition of MFs and quick reliable grading of meningioma. Fifty-four archival meningiomas (26 benign, 20 atypical, 8 anaplastic) were reclassified according to cur-rent WHO criteria. PHH3-immunostained MFs were counted the same way as in hematoxylin and eosin-stained sections. Anti-PHH3-labeled MFs were easily seen and permitted quick identification of the area(s) of highest mitotic activity. Count results (mean) show a strong correlation between both methods: benign, hematoxylin and eosin 1.4, PHH3 2.2; atypical, hematoxylin and eosin 9.0, PHH3 15.9; anaplastic, hematoxylin and eosin 22.4, PHH3 34.1. PHH3 counting yielded greater sensitivity and in 12 cases (22.2%) suggested a change in grade (increased 9; lowered 3). All cases in which PHH3 lowered the grade were from older blocks, suggesting a loss of antigen preservation. PHH3 immunostaining facilitates the rapid reliable grading of meningiomas by focusing attention on the most mitotically active areas and by allowing easy and objective differentiation of MFs from apoptotic nuclei.