P553: preliminary results of mrd analysis of aml1718, a phase 2 open-label study of venetoclax, fludarabine, idarubicin and cytarabine (v-flai) in the induction therapy of non low-risk aml

Background: The Italian AML1718 trial (NCT03455504) investigating the safety and efficacy of the BCL-2 inhibitor venetoclax (VEN) in combination with Intensive fludarabine-based induction (FLAI) [fludarabine 30 mg/sqm from day 1 to day 5, cytarabine 2000 mg/sqm from day 1 to day 5, and idarubicin 8 mg/sqm on days 1, 3 and 5] as first-line therapy for newly diagnosed non low-risk ELN adult Acute Myeloid Leukemia (AML) patients recently completed enrolment. Results from the Planned Interim Analysis of Safety Run-in and Part 1 (early expansion cohorts) were recently presented at 2022 ASH Meeting showing promising results in terms of complete remission rates (CR) and overall survival (OS). With a median follow-up of 10.5 months, 28 patients (49%) received HSCT in CR. Median overall survival (OS) was not reached; probability of 12-month OS was 76%. Median disease-free survival was not reached. Aims: Here we report the preliminary results of the centralized multicolour flow cytometry minimal residual disease (MFC-MRD) analysis performed during the phase 2, part 2, of the study (confirmatory cohort) where the lower effective dose of VEN (400 mg/day) was administered in association with FLAI, focusing on early MRD time-points (TPs) with the aim of identify the most informative TP for MRD evaluation. Methods: Erythrocyte-lysed whole bone marrow (BM) samples obtained at diagnosis from patients enrolled in the confirmatory cohort were centralized and analysed with a broad panel of monoclonal antibodies to identify the leukemia-associated phenotype (LAIP) which was used to track residual leukemic cells during follow-up. Eight colour flow cytometry analysis was performed at pre-defined TPs (TP1: post-induction I, TP2: post induction II/consolidation I, following TPs: post consolidation/pre-transplantation) (FACSCantoII; BD Facs Diva Software V6.1.3). A positive flow MRD was defined by the presence of no less than 10 clustered leukemic cells/10^4 total events. Enrolment closed on January 2023 so that the collection and the analysis of post-induction and consolidation TPs is still ongoing. Results: 67 patients were enrolled in the phase 2, part 2. Risk stratification according to ELN 2017 was intermediate in 46% of patients and high risk in 54%. Fifty-eight/67 patients (87%) obtained CR after induction I. Regarding centralized MRD analysis 144 samples from 67 patients treated in 11 different centers has been collected and analysed so far. Baseline sample for MRD were available in 65/67 patient (97%). TP1 was available in 56/58 patient achieving CR (97%), and TP2 was available in 29/58 patient (50%), so far. In 11/144 (8%) of the analysed samples haemodiluition was present leading to a non-adequate MRD analysis. Most (10/11, 91%) of the samples presenting haemodiluition were obtained at day TP1 (day 28 post induction I) in patients with delayed haematological recovery (Fig. 1). MFC-MRD negativity was obtained in 40/56 (71.4%) at TP1 (post V-FLAI, Fig. 1). An increase in MFC-MRD negativity rate was observed at TP2 (post Induction II or consolidation I) with 28 MFC-MRD negative patients/29 available samples (96.5%, Fig. 1). Summary/Conclusion: Preliminary results from centralized MRD analysis confirm that the combination therapy is able to induce high-quality remissions with a very high percentage of MFC-MRD negativity in a difficult cohort of patients with a higher percentage of MFC-MRD-negative after the completion of the second course of therapy. As delayed haematological recovery due to the deep myelosuppression of V-FLAI is observed, the most reliable TP for MFC-MRD assessment appears to be TP2. Correlation with survival will be performed as the data collection will be complete. Keywords: Flow cytometry, Acute myeloid leukemia, High risk, Minimal residual disease (MRD)