Introduction/Background*The aim of this study was to assess the outcomes of a large series of patients treated conservatively for a stage II or III serous borderline tumors of the ovary (SBOTs) with a long-term follow-up.

Methodology Patients with SBOTs and peritoneal implants, treated in or referred to our institution, were retrospectively reviewed. Outcomes of patients treated conservatively (preservation of the uterus and at least a part of one ovary) to promote subsequent fertility were specifically analyzed.

Result(s)*Between 1971 and 2017, 212 patients were identified and followed-up. Among them, 65 underwent a conservative treatment. Eight patients had invasive implants. Among patients treated conservatively, 38 (58%) patients recurred. Twenty-eight recurrences were observed under the form of borderline tumor on spared ovary and/or noninvasive implants, but 8 patients had a recurrence under the form of invasive disease. Compared to radical surgery, the use of a conservative treatment (p<.0001) was a prognostic factors on disease free survival (DFS), but without impact on overall survival (OS). Nevertheless, 3 deaths occurred. Twenty-four pregnancies (13 spontaneous) were observed in 20 patients (29 patients wishing to be pregnant).

Conclusion*In this series collecting the largest number of patients undergoing conservative surgery for stage II/III SBOTs, spontaneous pregnancies can be achieved after conservative treatment of advanced-stage disease, but the recurrence rate is high, and 3 deaths were observed. These patients spared their fertility but with a high rate of recurrence. Uncertainties about safety of conservative treatment should be exposed to them.