Centralized MRD Assessment in Gimema AML1718 Trial, a Phase 2 Open-Label Study of Venetoclax Combined with Intensified FLAI Chemotherapy (V-FLAI) As Induction Therapy of Non Low-Risk AML

Background: New therapeutic strategies are strongly needed to improve the prognosis of high risk Acute Myeloid Leukemia (AML) patients. The Italian GIMEMA AML1718 trial (NCT03455504) investigated 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. The Planned Interim Analysis of Safety Run-in and Part 1 (early expansion cohorts) showed median overall survival (OS) not reached; probability of 12-month OS was 76%. Median disease-free survival not reached. With a median follow-up of 10.5 months, 28 patients (49%) received HSCT in complete remission (CR). Centralized multicolour flow cytometry minimal residual disease (MFC-MRD) assessment was planned during the phase 2, part 2 of the study (confirmatory cohort) where the lower effective dose of VEN (400 mg/day) was administered with FLAI. 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 (0.1% threshold). Enrolment closed on January 2023. Results: Sixty-seven patients from 11 centers were enrolled in the phase 2, part 2. Median age 55 (22-66). Risk stratification according to ELN 2017 was intermediate in 52% and high risk in 48%. Ten patients harboured FLT3-ITD mutation (17.3%). Forty-seven/ 62 evaluable patients (76%) obtained CR after induction I. Regarding centralized MRD analysis 170 samples has been collected and analysed (60 baseline samples, 110 MRD samples). Seven patients lacking baseline sample for LAIP identification were excluded from the analysis. TP1 and TP2 MRD assessment were scheduled at day 28 of Induction I and Induction II/consolidation, respectively. However, in most cases, delayed haematological recovery was observed after V-FLAI leading to suboptimal timing of MRD evaluation. TP1 was available in 47/47 patient achieving CR (100%), and TP2 was available in 31 patients. Thirteen/110 samples for MRD analysis (8%), albeit resulting MRD negative, were considered inadequate for the analysis due to haemodilution, 6 from TP1 and 2 from TP2 and 5 from subsequent timepoints. MFC-MRD negativity was obtained in 27/41 evaluable samples (65.8%) at TP1 (post V-FLAI,). An increase in MFC-MRD negativity rate was observed at TP2 (post Induction II or consolidation I) with 23 MFC-MRD negative patients/27 evaluable samples (85.2%). MRD negativity probability at TP1 was not affected by ELN risk score or presence of FLT3-ITD mutation (p=n.s.). A total of 38/67 (56,7%) patients proceeded to allogeneic stem cell transplantation (HSCT) after FLAI-V, 20/38 (52%) patients received HSCT in MRD negative status. After a median follow-up of 22.08 months (IQR 11.04-31.11), 1-year overall survival (OS) was 53% and 1-year disease free survival (DFS) was 60%. Achieving MRD negativity resulted in a significantly better DFS (1-year DFS of 69% and 28%, in MRD negative or positive patients, respectively, p<0.01), whereas there was a trend towards longer OS in MRD negative patients (1-year OS of 70% and 47%%, in MRD negative or positive patients, respectively, p=0.051) Conclusions: Preliminary results from centralized MRD analysis confirm that the combination therapy was able to induce MRD negative CR in the majority of patients in our difficult cohort. MRD negativity probability was not affected by ELN risk or FLT3-ITD mutations. Achieving a negative MRD status resulted in a longer survival. Delayed haematological recovery may impact on reliability of MRD assessment due to hypocellular and regenerative marrow samples, so that the timing of assessment should be carefully chosen in each patient.