Abstract CT088: Phase I/II study of the PARP inhibitor olaparib in combination with irinotecan in children with advanced malignancies: arm D of the AcSé-ESMART trial

Abstract Background: AcSé-ESMART is a proof-of-concept, phase I/II, platform trial, designed to explore targeted agents in a molecularly enriched relapsed/refractory pediatric population. Arm D was evaluating the PARP inhibitor (PARPi) olaparib (ola) in combination with irinotecan (iri). In contrast to other PARPi/chemotherapy combination studies, we opted for a prolonged course of PARPi and low dose irinotecan as sensitizer. The Phase I part previously established the recommended Phase II dose (RP2D) (Gatz ASCO 2019). This is the report of the Phase II part of the trial assessing the activity in two separate expansion cohorts: cohort 1: homologous recombination repair defect (HRD) and cohort 2: Ewing sarcoma (ES). Methods: Ola was administered orally twice daily at 90 mg/m2 on Days 1 to 10 and iri intravenously at 20 mg/m2 on Days 4 to 8 of a 21-day cycle. Activity assessment followed a Minimax Simon 2-stage design. Each cohort was to progress to the second stage (additional 9 patients) if 2 or more confirmed responses were observed in the first 16 patients. Patients treated in the Phase I part at the RP2D were counting towards the respective expansion cohorts. Results: Seventy patients (median age: 14 years, range 5-23) were included in the whole study, 67 received treatment; 27 patients were treated in the dose escalation part, including 10 at the RP2D (8 in cohort 1 and 2 in cohort 2). Both cohorts passed the 1st stage and a total of 24 and 26 patients were recruited to cohort 1 and 2, respectively. Main diagnoses in cohort 1 were sarcoma (n=10), brain tumor (n=9), neuroblastoma (n=4). In cohort 1, 15 of 24 patients were considered enriched based on molecular alteration at relapse (ATM n=6; BRCA1 n=2; DNA signature 3 n=3; FANCD2, CHEK2, FANCA, ATRX all n=1); all patients in cohort 2 had presence of a ES fusion (ESWR1::FLI1 n=22; EWSR1::ERG n=4). Median number of treatment cycles were 2, range 1;51 in cohort 1 and 1;32+ in cohort 2. In cohort 1, 3 patients had a partial response (PR) (pinealoblastoma, neuroblastoma, choroid plexus carcinoma; treated with 12, 51, 25 cycles), 1 patient an unconfirmed PR (rhabdomyosarcoma, 6 cycles) and 7 patients stable disease (SD) (2 prolonged with 6 and 8 cycles). In cohort 2, 1 patient had a complete response (10 cycles) and 1 a PR (32+ cycles), 7 patients had SD (3 prolonged with 6, 10, 16 cycles). Molecular enrichment did not predict response. Retrospective correlative analysis of the molecular profiling data and tumor tissue expression analysis are ongoing to identify predictive biomarkers for PARPi combination trials and data will be presented. Conclusions: Encouraging clinical benefit was observed with the protracted ola-iri schedule in a subset of patients. Current molecular hypothesis is insufficient for patient selection and better biomarkers are needed. Citation Format: Susanne A. Gatz, Pablo Berlanga, Baptiste Archambaud, Yassine Bouchoucha, Nicolas André, Nadege Corradini, Windy Rondof, Jonathan Rubino, Souad Nebchi, Antonin Marchais, Estelle Thebaud, Alba Rubio San Simón, Natasha K. van Eijkelenburg, Lynley V. Marshall, Anne-Sophie Defachelles, Adela Canyete, Stephane Ducassou, Guy Makin, Michela Casanova, Emilie De Carli, Arnaud Petit, Gwenael Le Teuff, Xavier Paoletti, Peter G. Mortimer, Gilles Vassal, Birgit Geoerger. Phase I/II study of the PARP inhibitor olaparib in combination with irinotecan in children with advanced malignancies: arm D of the AcSé-ESMART trial [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 2 (Clinical Trials and Late-Breaking Research); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(8_Suppl):Abstract nr CT088.