Introduction/Background Low-grade endometrial stromal sarcoma (LG-ESS) is an extremely rare uterine malignant neoplasm and belongs to the WHO-classification of endometrial stromal neoplasms. In rare cases, the tumor can arise from extra-uterine localizations, e.g. from endometriosic lesions. Malignant findings in endometriosis are extremely rare (0.7–0.1%) with ESS being the least common malignancy.

Methodology We present a 32-year-old woman with LG-ESS arising from deep-infiltrating endometriosis (DIE). Initial symptoms, imaging modalities, histological findings, disease progression, operation technique and the outcome after final surgery are reported.

Results The patient presented with two indolent solid masses in the lower abdomen coincidentally detected by a routine ultrasound. The MRI displayed multiple T2 hyperintensities with diffusion disturbance in the adjacing peritoneum. The diagnostic laparoscopy revealed multiple hypervascularized lesions in the lower and upper abdominal cavity and a biopsy was performed. The immunohistochemical workup of the biopsy showed strong nuclear positivity for WT1, ER and PR and partial positivity for CD10 and CD34 in the stroma, leading to the diagnosis of LG-ESS arising from DIE. Three months later the follow-up MRI deteced a tumor progression. For oncologic safety, a maximum cytoreductive surgery without fertility preservation (TH-BSO, omentectomy, peritoneal biopsy, excision of additional suspect findings) was performed, achieving a macroscopically complete resection of the tumor and the DIE. The final immunohistochemical results showed metastases in the uterine peritoneum but not in the uterine stroma, thus most likely the LG-ESS arose from foci of endometriosis.

An adjuvant endocrine therapy with aromatase inhibitors was initiated. Six months later in a follow-up MRI no tumor recurrence was seen.

Conclusion LG-ESS arising from endometriosis is a very rare condition, and to date no standard therapy has been established. However, it can be concluded from the literature that complete surgical resection is a significant positive prognostic factor for recurrence and survival.

Disclosures none