['It has been suggested that p16 is overexpressed in uterine leiomyosarcomas in comparison with leiomyomas. In this study, p16 immunohistochemical expression was assessed in a variety of uterine smooth muscle tumours, including usual leiomyomas, leiomyoma variants, smooth muscle tumours of uncertain malignant potential (STUMPs) and leiomyosarcomas. The aim was to ascertain whether there are differences in p16 expression between these groups and whether p16 is of potential value in the assessment of problematic uterine smooth muscle neoplasms. p16 expression was also compared with that of p53 and MIB1.', 'Cases of usual leiomyoma (n = 10), leiomyoma variants (n = 27), STUMP (n = 4) and leiomyosarcoma (n = 22) were subject to p16, p53 and MIB1 immunohistochemistry. For p16, cases were evaluated with respect to both staining distribution and intensity. There was a statistically significant difference in p16 distribution (P < 0.001) and intensity (P = 0.001) between leiomyosarcomas and the other groups. There was no difference in p16 expression between usual leiomyomas, leiomyoma variants and STUMPs. There were also statistically significant differences in p53 (P = 0.014) and MIB1 (P < 0.001) immunoreactivity between leiomyosarcomas and the other groups.'] Are uterine leiomyosarcomas characterized by high p16 , p53 and MIB1 expression in comparison with usual leiomyomas , leiomyoma variants and smooth muscle tumours of uncertain malignant potential?