ITCC-101/APAL2020D: A randomized Phase 3 trial of fludarabine/cytarabine/gemtuzumab ozogamycin with or without venetoclax in children with relapsed Acute Myeloid Leukemia

Abstract Background Despite improvements in the treatment of children with acute myeloid leukemia (AML) with modern multi-agent therapy, survival after relapse remains poor. Outcomes are particularly suboptimal for patients unable to receive anthracycline-based salvage therapies due to prior cardiac toxicity or maximal cumulative exposure. More effective and less toxic therapeutic options for these groups of children are needed. Venetoclax is a potent, orally bioavailable B-cell lymphoma-2 (BCL-2) inhibitor that restores programmed cell death in cancer cells. Venetoclax is approved in Europe and the United States for adults with newly-diagnosed AML ineligible for intensive chemotherapy and is frequently used in combination with hypomethylating agents or cytarabine-based chemotherapy, but is not approved for use in children. Prior pediatric-specific investigation via the VENAML phase 1/2 trial demonstrated safety and activity of venetoclax in combination with idarubicin and/or high-dose cytarabine in children with multiply-relapsed/refractory AML (Karol et al., Lancet Oncology 2020). The ITCC-101/APAL2020D open label randomized phase 3 clinical trial (EUCTR 2023-510160-12-00, NCT05183035) is now studying the therapeutic efficacy of fludarabine/cytarabine (FLA) and gemtuzumab ozogamicin (GO) without or with venetoclax in pediatric patients with relapsed AML within the framework of a pediatric investigational plan and written request agreement. Design and Methods Patients >28 days and <22 years of age with second medullary/combined relapsed AML or first relapse unable to receive further anthracyclines are eligible to participate in APAL2020D with an initially-planned total enrollment of 98 randomized subjects. Cycle 1 chemotherapy is FLA/GO, and Cycle 2 is FLA. Patients are further randomized to no venetoclax (control arm A) or additional receipt of venetoclax for 21 days per cycle (experimental arm B) at 300 mg adult equivalent dose [AED] on Cycle 1 Day 1, then 600 mg AED daily on Cycle 1 Days 2-21 and in Cycle 2 Days 1-21. Patients who achieve complete remission +/- incomplete count recovery or platelet recovery (CR/CRi/CRp) after Cycle 2 may proceed to subsequent allogeneic hematopoietic stem cell transplantation (HSCT). Patients unable to proceed to HSCT may receive azacitidine without or with venetoclax daily continuously at 400 mg AED for up to 24 cycles. The primary study objective is comparison of overall survival of pediatric patients treated with venetoclax and FLA/GO in arm B versus FLA/GO in arm A. The primary analysis will be performed at approximately five years from the first patient randomization. Secondary objectives include assessment of safety, venetoclax pharmacokinetics, event-free survival, rates of measurable residual disease (MRD)-negative CR/CRi/CRp, and percentage of patients who proceed to subsequent HSCT. Exploratory objectives include performance of various correlative biomarker studies, including BCL-2 homology profiling and venetoclax drug sensitivity. Bone marrow response assessments by morphology and flow cytometric MRD are performed in centralized reference laboratories. Study updates APAL2020D is currently open at 80 sites across 20 countries in Australia, Europe, Israel, Japan, New Zealand, and North America. Ten additional sites in Europe and North America are in process of study activation. Four data safety monitoring board meetings have occurred to date, and early safety stopping rules have not been met. Several study changes have been implemented via protocol amendments, including updated chemotherapy safety information and adverse event monitoring, clarification of study procedures, and revision of response terminology and demographic data collection in response to guidance from federal agencies. As of 1st August 2025, a total of 71 patients has been enrolled on APAL2020D (n=34 in arm A, n=37 in arm B). To date, 33 of 71 patients (46%) have enrolled in the late first relapse (LFR) cohort, while 28 (40%) and ten (14%) study patients are in early first relapse (EFR) or second relapse (SR) cohorts, respectively. This distribution deviates from the originally anticipated rates of 20% EFR, 15% LFR, and 65% SR. In particular, the proportion of patients enrolled with LFR was substantially higher than expected (46% compared to 15%). Given the relatively more favorable prognosis of children with AML in LFR, an amendment for potential study enrolment expansion is under consideration.