Introduction/Background Borderline ovarian tumors represent 15% of ovarian tumors. The difficult differential diagnosis with ovarian neoplasia makes its management and treatment important. Recurrences of borderline tumors can appear years after the initial treatment and neoplastic cells can be found, although they usually present the same histology as the primary tumor.

Study objectives •Main objective: to describe the recurrence rate of borderline ovarian tumors in our center.

•Secondary objectives: define histology, type of surgery, risk factors for recurrence, and disease survival

Methodology Single-center retrospective observational study. Patients treated for a borderline ovarian tumor and who are under follow-up at our center between 1993 and 2023 were reviewed.

Results A total of 89 cases were reviewed. Average age at diagnosis of 48 years (16–86 years)

Histology of the tumors: 68.5% mucinous tumors, 30.3% serous tumors, 1.1% other histologies

Tumor stage 70.8% Stage IA, 1.1% Stage IB, 22.4% Stage IC, 1.1% Stage IIB, 2.2% Stage IIC, 2.2% Stage IIIC

In 93.3% of cases, no neurovascular or stromal invasion was detected.

In 9% of the tumors there were foci of intraepithelial or invasive carcinoma.

Radical surgery was performed in 53% of cases.

42.3% of the patients had high pre-surgical CA125 levels, with a mean of 212.26 U/ml.

In the follow-up of our series, in these 23 years, we have detected 3 cases of recurrence (2.67% of the total).

We have not found risk factors for recurrence in our patients.

Overall survival is 100%.

Conclusion In our series, the majority of borderline tumors were diagnosed at stage I (94%), with an overall survival of 100% and a very low recurrence rate (2.67%).

In the cases that have recurred, we have not found any risk factor for recurrence, and this has occurred before 10 years.

Disclosures No.