Introduction/Background A 44-year-old woman with a history of ovarian cystectomy due to endometriosis in 2012; endometrioma of 4 cm in september 2022 with Ca125 220 and Ca19.9 74.

In September 2023, attended the hospital for severe abdominal pain.

A CT scan was requested, which described an ovarian mass measuring 15 x 10 x 13 cm in the left adnexal area. The MRI showed an enlargement of left paraovarian endometriotic involvement that extends through the pelvis, in the anterior region of the uterus. Deep endometriosis in Douglas and bilateral endometriomas.

In october come to our center for a second opinion, and was schedule for primary debulking surgery.

Methodology A few days later, prior to Scheduled Surgery, presents pain that is difficult to control and difficult feeding. In the face of clinical worsening and progressive anemia, emergency surgery is indicated.

A Friable and vascularized abdominal tumor of 30 cm was evidenced, firmly adhered to parietal peritoneum, mesentery root peritoneum, vesicouterna plica, right flank and appendix, omentum and loop of jejunum. Due to the firm adhesions, rupture of the mass occurs with profuse bleeding that is resolved with ligation of vascular pedicles of the uterus and ovaries. In addition, 1 cm tumor-like nodules in Morrison’s space and cardiophrenic fat are evidenced . Complete debulking was performe

Results The anatomopathological analysis revealed a high grade sarcoma on an endometrial focus. : FISH: YWHAE negative. BCOR negative No RNA translocation.

Conclusion Therefore, it was considered an undifferentiated sarcoma on the endometriosis focus.

Three weeks after surgery, peritoneal implants in abdominal ultrasound were suspected, and confirmed by CT scan, which revealed the presence of multiple peritoneal and extraperitoneal tumor implants as well as pathological lymphadenopathy in iliac territories. Ca125 on the rise (373 U/ml).

Disclosures In view of the rapid growth of lesions, it is proposed to initiate first line of chemotherapy with palliative intent with Epirubicin + Ifosfamide.