spindle cell sarcoma chemotherapymetastatic endometrial stromal sarcomaendometrial stromal sarcoma pathologyendometrial stromal sarcoma cancerendometrial stromal sarcoma stage 4endometrial sarcomaendometrial stromalspindle cell neoplasm treatmentspindle cell tumors treatmentstromal sarcoma uterusundifferentiated endometrial sarcomametastatic endometrial sarcoma