RT Journal Article SR Electronic T1 EP906 Pre-operative prediction of residual disease after interval debulking surgery for advanced stage epithelial ovarian cancer using a multivariable model with HE4 JF International Journal of Gynecologic Cancer JO Int J Gynecol Cancer FD BMJ Publishing Group Ltd SP A488 OP A488 DO 10.1136/ijgc-2019-ESGO.952 VO 29 IS Suppl 4 A1 Lof, P A1 van de Vrie, R A1 Korse, CM A1 van Driel, WJ A1 Gent, MDJM van A1 Karlsen, MA A1 Amant, F A1 Lok, CAR YR 2019 UL http://ijgc.bmj.com/content/29/Suppl_4/A488.1.abstract AB Introduction/Background Presence of residual disease (RD) after interval debulking surgery (IDB) is an important negative prognostic factor for patients with advanced stage epithelial ovarian cancer (EOC). Surgery is of limited benefit when the diameter of RD is >1 cm. RD is difficult to predict before surgery. The multivariate model Cancer Ovarii Non-invasive Assessment of Treatment Strategy (CONATS) index, based on serum biomarker Human Epididymis 4 (HE4), age and WHO performance status (PS), predicted no visible RD in patients undergoing primary debulking surgery with an AUC of 0.85. The AUC of predicting RD >1 cm was not reported, although this can be of importance for pre-operative decision making especially in fragile patients. We tested this model for predicting RD >1 cm in patients undergoing IDB.Methodology We retrospectively included patients with advanced EOC who underwent IDB between 2010 and 2017 in two tertiary centers in the Netherlands. HE4 was measured with electrochemiluminescence in pre-operative samples. The CONATS-index was used to predict RD. Areas under the curve (AUC) were calculated to predict RD >1 cm.Results Two-hundred-seventy-three patients were included. Mean age was 64 years (SD 11 years). Following surgery, 232 patients (85%) had RD ≤1 cm and 41 patients (15%) had RD >1 cm. The AUC was 0.80 for predicting RD >1 cm. In patients ≥70 years of age the AUC was 0.82.Conclusion The CONATS-index can help to predict surgical outcome after IDB in addition to radiologic parameters and can be useful in counseling patients about the chance whether a meaningful IDB can be achieved. This could be especially helpful in counseling elderly patients in whom surgery has an increased risk of complications.Disclosure Nothing to disclose.Abstract EP906 Figure 1 The ROC of the CONATS-index, HE4, CA125 and age for predicting >1 cm RD after IDB