The Accuracy of pHH3 in Meningioma Grading: A Single Institution Study

Introduction: In the latest WHO classification of central nervous system tumors, Mitotic Index (MI) counted on Phosphohistone-H3 stained slides (pHH3-MI) has been suggested as a valid proliferative marker in various tumors including in the evaluation of meningioma grading. We aim to report our own experience in assessing the efficiency of the anti-pHH3 antibody as a grading tool for meningiomas. Methods: A retrospective study was conducted on a series of 40 meningiomas diagnosed from March 2020 to April 2021 at the Pathology Department of the Military Hospital of Tunis. We attempted immunohistochemistry and compared MI assessed on both pHH3 and HE-stained slides. Results: According to the HE-MI and pHH3-MI, the 40 cases of meningiomas were respectively divided into 35 versus 29 grade 1 cases, four versus eight grade 2 cases, and one versus three grade 3 cases. A highly significant correlation was found between pHH3-MI and HE-MI (p < 0.001). A significantly higher sensitivity in the pHH3 counting method was reported in our study. Discussion: we found, in accordance with the literature, that pHH3-MI is more reliable and accurate in mitotic counting, therefore exhibiting a high sensitivity in tumor grading, reported by an upgrade within 22,5% of the cases. Conclusion: PHH3-MI count facilitated a rapid reliable grading of meningiomas. However, molecular characteristics that could have a potentially significant impact on tumor progression should be the subject of further research.