Evaluation of Phosphohistone H3 in Assessment of Mitotic Activity in Invasive Breast Carcinoma: A Correlative Study With Ki-67 and Histologic Grade

Background Accurate assessment of tumor proliferation is vital for grading breast cancers, which impacts prognosis. Phosphohistone H3 (PHH3) is a mitotic figure-specific immunohistochemical (IHC) marker. This study aims to evaluate the utility of PHH3 in detecting mitotic figures in invasive breast carcinoma in comparison to the conventional counting on hematoxylin and eosin (H&E) slides and its correlation with Ki-67 index, histological grade, and other clinicopathological parameters. Materials and methods The study was conducted on 100 mastectomy specimens with breast cancers. Tumors were graded using the Nottingham grading system. IHC staining was performed for PHH3 and Ki-67. Results In 40% of specimens, the PHH3 score was elevated (>13 mitotic figures per 10 HPF). PHH3 identified significantly higher mitotic figures than conventional H&E (14 vs 7/10 HPF) and this led to a shift toward higher grades. By H&E, 41% of tumors were grade 2, 40% grade 1, and 19% grade 3. After the PHH3 reassessment, grade 1 dropped to 34%, while grade 3 rose to 31%. PHH3 score significantly correlated with mitotic score on H&E ( p < 0.001), nuclear pleomorphism ( p = 0.008), tumor grade ( p < 0.001), and Ki-67 index ( r = 0.534, p < 0.001). Cohen's kappa value was 0.194 for H&E (poor agreement) and 0.463 for PHH3 (moderate agreement), indicating improved inter-observer concordance with PHH3. Conclusion By highlighting the mitotic figures, PHH3 identified increased mitotic figures resulting in the upgrading of tumors. Its incorporation into routine practice may aid in accurate tumor grading and precise prognostic stratification.