PT - JOURNAL ARTICLE AU - Hanine Medani AU - Mohamed Elshiekh AU - Kikkeri N Naresh TI - Improving precise counting of mitotic cells in mantle cell lymphoma using phosphohistone H3 (PHH3) antibody AID - 10.1136/jclinpath-2020-206956 DP - 2020 Sep 01 TA - Journal of Clinical Pathology PG - jclinpath-2020-206956 4099 - http://jcp.bmj.com/content/early/2020/08/31/jclinpath-2020-206956.short 4100 - http://jcp.bmj.com/content/early/2020/08/31/jclinpath-2020-206956.full AB - Aims Mantle cell lymphoma (MCL) has a highly heterogeneous clinical course ranging from indolent, to aggressive and rapidly progressive disease. Proliferation is a strong predictor for disease outcome. In routine clinical practice, Ki-67 expression is used as a measure of proliferation. However, several studies have documented a high degree of inter-laboratory and inter-observer variation with Ki-67 immunohistochemistry. Phosphorylation of histone H3 occurs specifically during mitosis and hence serves as a specific marker for cells in mitosis.Methods and results We investigated phosphohistone H3 (PHH3) immunohistochemistry as a proliferation maker in 28 tissue biopsies of MCL and compared the PHH3 results (as evaluated by direct microscopic visualisation and image analysis-aided scoring) with morphological subtyping, mitotic counts and Ki-67 index. We found PHH3-mitotic count was about sixfold higher than H&E-mitotic count (mitoses in 10 high power fields). Furthermore, PHH3-mitotic count in aggressive morphological variants of MCL was significantly higher than in usual MCL. The PHH3-mitotic count showed a strong linear correlation with PHH3-mitotic index (percentage positive cells).Conclusions We found PHH3 immunohistochemistry, a reliable mitosis-specific marker, in MCL. Performing precise counts and evaluating precise proliferation indices is easier with PHH3 immunohistochemistry. This contrasts with the conventional estimation of Ki-67 percentages by ‘eye-balling’.