562 Benefit from Atezolizumab in Patients with a Poor Prognostic Ovarian Cancer in First-Line Setting: IMAGYN-050 Trial

Introduction/Background Adding the anti-PD-L1 immune-checkpoint-inhibitor (ICI), atezolizumab, to first-line chemotherapy + bevacizumab did not improve PFS for unselected ovarian cancer (OC) patients in IMAGYN-050 phase III trial. In the GCIG meta-analysis, the patients with a poorly chemosensitive disease (unfavorable KELIM score <1.0) that was not amenable to optimal surgery had a very poor survival. We hypothesized that KELIM may help identify a particularly poor prognostic patient subgroup deriving a PFS benefit from treatment intensification with the ICI atezolizumab. Methodology This post-hoc analysis was performed on 1,199 participants treated with atezolizumab (n=597) or placebo (n=602) with ≥3 CA125 measurements. Independent prognostic factors were identified using univariate/multivariate analyses among following covariates: Disease stage (III/IV); Pathological subtype; ECOG performance-status; Chemotherapy-setting (neo-adjuvant/adjuvant); Surgery outcome (optimal/sub-optimal resection); PDL-1 expression (positive/negative); BRCA mutation (mutated/wild-type); and KELIM score (unfavorable<1.0/favorable≥1.0). The PFS benefit from atezolizumab addition (vs.placebo) was tested in patients with both an unfavorable KELIM score<1.0 and a sub-optimal surgery (once validated as independent prognostic factors). Results Univariate and multivariate analyses confirmed that both KELIM score (favorable/unfavorable, HR=0.61, 95%CI 0.54–0.69) and surgery outcome (sub-optimal/optimal, HR=1.41, 95%CI 1.19–1.67) were independently associated with PFS. Adding atezolizumab to frontline regimen was associated with longer PFS in the poor prognosis subgroup (n=269) characterized by both an unfavorable KELIM score and sub-optimal cytoreduction (median PFS: 14.3 vs 11.3 months, HR=0.75, 95%CI 0.59–0.95, P=0.02), and consistent in both neo-adjuvant/adjuvant settings. No significant PFS benefit was observed from atezolizumab with KELIM score assessed alone, or among the other prognostic subgroups. Conclusion In IMAGYN-50 trial, the poor prognostic subgroup of ovarian cancer patients (unfavorable KELIM score <1.0 and sub-optimal surgery), might have derived a significant PFS benefit from the treatment intensification with the ICI atezolizumab. These outcomes on the largest phase III trial dataset open new perspectives about the best population for immunotherapy addition. Disclosures BY: Consulting for MSD, Astra-Zeneca, GSK-TESARO, BAYER, Roche-Genentech, ECS Progastrine, Novartis, LEK, Amgen, Clovis Oncology, Merck Serono, BMS, SEAGEN, Myriad, Menarini, Gilead, EISAI. PT: Grants or consulting: GSK, Merck, UpToDate, Versastem, Caris, AZ, Clovis, ZEntalis, Immunogen, Addi Biopharma, Seagen, Immunon. Stock holder: Immunon CA: Clinical trial funding to institution (MSK): Abbvie – MSK PI, GOG3005; Astra Zeneca - MSK PI, SOLO1/GOG 3004; National Coordinating Investigator & MSK PI, D081RC00001; ENGOT-ov46; AGO-OVAR 23; GOG-3025; Clovis – MSK PI, ARIEL 2 & 3; Genentech/Roche – MSK PI, GOG3015 (IMagyn050). Consulting: Blueprint Medicine – Advisory Board 6/30/21 (no consulting fee); Merck - Global Cervical and Ovarian Cancer Virtual Advisory Board 7/10/23; AstraZeneca - AZ eVOLVE DMC 4/26/23-ongoing JF: Educational activities, GSK and Astra Zeneca TM: Immunogen YGL is employed by Roche-Genentech and stock shareholder YH was employed by Roche-Genentech All other coauthors disclose no conflict of interest.