PT - JOURNAL ARTICLE AU - Scambia, Giovanni AU - Vergote, Ignace AU - Hamilton, Erika AU - Fidalgo, Jose Perez AU - Gorp, Toon Van AU - Sehouli, Jalid AU - Klat, Jaroslav AU - Levy, Tally AU - Welch, Stephen AU - Richardson, Debra AU - Alía, Eva Guerra AU - Henry, Stéphanie AU - Wimberger, Pauline AU - Miller, David AU - Martínez, Jerónimo AU - Monk, Bradley AU - Kalyanapu, Pratheek AU - Mirza, Mansoor Raza AU - Makker, Vicky TI - PO006LBA/#1520  Selinexor maintenance for patients with TP53WT advanced or recurrent endometrial cancer: long-term follow up of efficacy and safety subgroup analysis of the ENGOT-EN5/GOG-3055/SIENDO study AID - 10.1136/ijgc-2023-IGCS.6 DP - 2023 Nov 01 TA - International Journal of Gynecologic Cancer PG - A5--A5 VI - 33 IP - Suppl 4 4099 - http://ijgc.bmj.com/content/33/Suppl_4/A5.short 4100 - http://ijgc.bmj.com/content/33/Suppl_4/A5.full SO - Int J Gynecol Cancer2023 Nov 01; 33 AB - Introduction Molecular characterization is important to inform treatment decisions for patients with endometrial cancer (EC). Wild type TP53 (TP53wt) is found in ~50% of advanced/recurrent EC and of those, ~70% are microsatellite stable (MSS/pMMR).Methods ENGOT-EN5/GOG-3055/SIENDO (NCT03555422) is a randomized double-blind, phase 3 trial evaluating selinexor vs placebo as a maintenance treatment for advanced/recurrent EC following response to prior systemic therapy. Here we report the updated efficacy and safety of a prespecified exploratory subgroup analysis of patients with TP53wt EC.Results 113 patients with TP53wt EC received selinexor (n=77) or placebo (n=36) as maintenance therapy. As of March 2023, the median follow-up was 25.3 months, and 26 patients remain on treatment. Median PFS (mPFS) was 27.4 months with selinexor vs 5.2 months with placebo (HR 0.42; 95% CI [0.25–0.70], nominal one-sided p=0.0003). PFS improvement was observed regardless of microsatellite instability status; in the TP53wt/MSS(pMMR) subgroup, the mPFS was not reached with selinexor vs 4.9 months with placebo. In patients with TP53wt, the most common adverse events (AEs) were nausea, vomiting, and diarrhea; most common grade ≥3 AEs were neutropenia, thrombocytopenia, and nausea; 16% of patients discontinued selinexor due to AEs. No grade 5 AEs occurred. No immune-related AEs were observed.Abstract PO006LBA/#1520 Figure 1 Conclusion/Implications TP53wt status may represent a robust predictive biomarker for selinexor efficacy in EC. Additionally, a strong PFS signal was observed in the TP53wt/MSS(pMMR) subgroup, a patient population with high unmet need. Both additional data and updated data will be presented at the conference.