Low-grade extrauterine endometrial stromal sarcoma of the peritoneum: A case report and literature review.

Endometrial stromal sarcoma (ESS) is an uncommon mesenchymal tumor that accounts for less than 1% of all primary uterine malignancies and extrauterine endometrial stromal sarcoma (EESS) is even rarer. We report the case of a 75-year-old woman with an abdominal tumor and multiple peritoneal implants. Histological analysis of the surgical specimens showed bland cellularity resembling normal endometrial stroma. The diagnosis of a low-grade EESS was confirmed by immunophenotypic findings and demonstration of JAZF1 translocation. After extensive sampling, no evidence of endometriosis was found. Our case showed atypical aggressive behavior and we discuss the possible influence of the high mitotic count (8/10 HPFs) in some areas of the tumor, the multifocality of the abdominal implants and the postmenopausal status of the patient. The unusual clinical presentation and extrauterine location of such a rare tumor were challenging implying a wide range of differential diagnosis. The correlation of morphological, immunohistochemical and molecular findings was necessary to arrive at the correct diagnosis.