Use of oxytocin receptor expression in distinguishing between uterine smooth muscle tumors and endometrial stromal sarcoma.

The present study aimed to investigate oxytocin receptor (OTR) expression in the normal uterus, and particularly in uterine smooth muscle tumors and endometrial stromal sarcomas (ESSs) because these tumors can be difficult to distinguish. The expressions of OTR, CD10, h-caldesmon, calponin, smooth muscle actin, and desmin were analyzed in 10 conventional leiomyomas (LMs), 10 highly cellular leiomyomas (HCLs), eight leiomyosarcomas (LMSs), and nine ESSs. In five normal uteri and five cases of adenomyosis, OTR was strongly expressed in the myometrium and showed expression pronounced in the surface epithelium during the late proliferative phase and at the time of ovulation, whereas the endometrial stromal cells were negative. All LMs and HCLs were strongly positive for OTR. Five cases of LMS showed moderate to strong OTR expression in 100% of the tumor cells, whereas three cases were weakly positive in 10-20% of the tumor cells. Every ESS was negative for OTR, except in regions of smooth muscle differentiation. All ESSs were positive for CD10, as were one LM, six HCLs, and five LMSs. The ESSs were negative for h-caldesmon and showed desmin positivity mainly in regions of smooth muscle metaplasia. h-Caldesmon, calponin, smooth muscle actin, and desmin were expressed in all LMs, HCLs, and LMSs except for one leiomyosarcoma with epithelioid features, which was negative for h-caldesmon and calponin. Our study indicates that the evaluation of OTR expression is useful in the distinction of uterine smooth muscle tumors from ESSs, and that the OTR is expressed in normal and neoplastic uterine smooth muscle cells.