BACKGROUND: The mitotic index is important in the assessment of tumors such as leiomyoma (LM) and leiomyosarcoma (LMS), which may exhibit a range of cytological atypia. The mitotic marker phosphohistone-H3 (PHH3) was shown to improve interobserver and intraobserver variability in many tumors. MATERIALS AND METHODS: We evaluated the mitotic index in 20 pilar LM and cutaneous LMS using PHH3 and hematoxylin and eosin (H&E)-stained sections. Ki-67 staining characteristics of the tumors were also assessed. RESULTS: Mitotic figures were more easily identified within PHH3 sections. The mitotic index per 10 high power fields (HPF) on the PHH3 stain was slightly higher than H&E both in the LM (mean 0.1, range 0-1 vs. mean 0) and LMS groups (mean 8.6 vs. 8.0 with range of 1-24 for both stains). The difference in mitotic index between the two stains was not statistically significant in either group (p = 0.7). The Ki-67 proliferative index showed a statistically significant correlation with a diagnosis of LMS. CONCLUSION: PHH3 immunostain can simplify counting of mitotic figures in cutaneous smooth muscle neoplasms, especially those with many pyknotic nuclei, and may help to reduce interobserver variability. Ki-67 staining may also be of help in establishing a diagnosis of LMS.
BACKGROUND: The mitotic index is important in the assessment of tumors such as leiomyoma (LM) and leiomyosarcoma (LMS), which may exhibit a range of cytological atypia. The mitotic marker phosphohistone-H3 (PHH3) was shown to improve interobserver and intraobserver variability in many tumors. MATERIALS AND METHODS: We evaluated the mitotic index in 20 pilar LM and cutaneous LMS using PHH3 and hematoxylin and eosin (H&E)-stained sections. Ki-67 staining characteristics of the tumors were also assessed. RESULTS: Mitotic figures were more easily identified within PHH3 sections. The mitotic index per 10 high power fields (HPF) on the PHH3 stain was slightly higher than H&E both in the LM (mean 0.1, range 0-1 vs. mean 0) and LMS groups (mean 8.6 vs. 8.0 with range of 1-24 for both stains). The difference in mitotic index between the two stains was not statistically significant in either group (p = 0.7). The Ki-67 proliferative index showed a statistically significant correlation with a diagnosis of LMS. CONCLUSION:PHH3 immunostain can simplify counting of mitotic figures in cutaneous smooth muscle neoplasms, especially those with many pyknotic nuclei, and may help to reduce interobserver variability. Ki-67 staining may also be of help in establishing a diagnosis of LMS.