Use of myocardin in the classification of mesenchymal tumors of the uterus.

It can sometimes be difficult to distinguish between the 2 main types of uterine mesenchymal neoplasms; uterine smooth muscle tumors (SMTs) and endometrial stromal sarcomas (ESSs), particularly when the ESSs show smooth muscle differentiation or the SMTs are highly cellular. The aim of this study was to investigate myocardin expression in normal uterus myometrium, in SMTs, and in ESSs and to determine whether myocardin can be used as a useful diagnostic tool in the classification of problematic uterine mesenchymal tumors. Immunohistochemical staining was performed in each group. Besides myocardin, all cases were also stained for other smooth muscle markers (h-caldesmon, desmin, smooth muscle actin) and for CD10. All tested markers were analyzed in 21 conventional leiomyomas (LMs), 21 highly cellular leiomyomas (HCLs), 12 leiomyosarcomas (LMSs), 3 endometrial stromal nodules (ESNs), 11 ESSs, and 15 normal uterus myometrium. Myocardin was expressed in all normal uterine myometrium and in SMTs (even in the regions with epithelioid features) moderately or strongly, at least topically, whereas in endometrium, in ESNs and in ESSs, except in the regions of smooth muscle differentiation, it was negative. All ESNs, 11 of 11 ESSs and 14 of 15 endometrium were negative for h-caldesmon, but all SMTs and normal uterine myometrium were positive for h-caldesmon except for 2 LMSs, 2 HCLs, and for the regions with epithelioid features in 2 LMs. Desmin was stained in all normal uterine myometrium and in SMTs (except those of the regions with epithelioid features), but it was negative in 1 HCL and 1 LMS. One of 3 ESNs and 2 of 11 ESSs were expressed in desmin. Smooth muscle actin was negative in all ESNs, 2 LMSs, and 2 HCLs, and positive in all myometriums, LMs (except for the regions with epithelioid features), 1 ESSs, and 1 proliferative phase endometrium. Eight of 11 ESSs and all ESNs were positive for CD10, as was 1 HCL, and 2 LMSs. All uterine myometrium, 3 ESSs, and 3 endometriums were negative for CD10. Our study indicates that the myocardin is expressed in normal and neoplastic uterine smooth muscle cells sensitively and that the evaluation of myocardin expression is useful in distinguishing SMTs from ESSs.