Summary

Malignant transformation on a background of endometriosis is rare and the primary site of the tumor is ovary in most of the cases although rare extragonadal cases have also been reported. The most common histopathologic tumor type is endometrioid carcinoma while sarcomas develop much more rarely. A case of low-grade endometrial stromal sarcoma arising on a background of endometrioid cyst of the ovary is presented in this paper. An adnexial mass was detected in a 52-year-old woman presenting with pelvic pain and surgical excision was performed. Macroscopically, the resected specimen was composed of a cystic mass measuring 15x10x10 cm and a histerectomy material 7x6x3 cm in dimentions. In addition, three solid masses, the biggest 4 cm in diameter were excised. Histerectomy specimen was unremarkable. Microscopic examination of the cystic and solid masses revealed a highly vascular tumor composed of diffusely arranged cells with oval or spindle-shaped nuclei. Less than 3 mitotic figures were counted on ten high-power-fields. Strong nuclear immunoreactivity in all of the tumoral cells was observed on the immunohistochemical staining for estrogen and progesteron receptors. The case was diagnosed as “Low-grade endometrial stromal sarcoma arising on a background of endometrioid cyst of the ovary”. No tumor was detected within the contralateral ovary, endometrium, myometrium or cervix. Differential diagnosis between extrauterine endometrial stromal sarcomas and the other spindle-cell tumors at the same localization may be difficult as the former are rare. The co-occurence with foci of endometriosis, similar histopathologic and immunohistochemical findings to their uterine counterparts help to make the diagnosis.