The Ki-67 nuclear antigen is associated with cell proliferation and found throughout the cell cycle; though not in G0 phase (1,2). The assessment of Ki-67 proliferation in breast cancers has shown the Ki-67 labelling index is an important predictor of survival (3).
Microscopic evaluation of mitotic figures on H&E is a routine procedure in the assessment of the tumor grades (4). However, the counting of mitosis is manual and time consuming with assorted difficulties as well as variabilities between interobserver assessments (5). Histone H3 phosphorylation at Serine10 (pHH3) is in association with mitotic chromatin condensation in late G2 and M phase of the cell cycle. pHH3 can distinguish mitosis from apoptotic nuclei (6). The immunohistochemical staining of Serine10-pHH3 has been reported to be comparable to mitotic figures in the H&E section (7-10).
Immunohistochemical studies have shown immunostaining using anti- Ki-67 and anti-pHH3 antibodies provided improved prediction of recurrence of tumors and may become effective ancillary tools in deciding on optimal therapeutic management (11). Other studies have shown Ki-67 and pHH3 can be useful in separating malignant melanoma from benign nevi (12).