Intensive Induction Chemotherapy with or without Gemtuzumab Ozogamicin Among Patients with Core-Binding Factor Acute Myeloid Leukemia

Background: Core-binding factor acute myeloid leukemia (CBF-AML) is characterized by the presence of inv(16)/t(16;16) or t(8;21), and is classified as favorable risk by the 2022 European LeukemiaNet (ELN) guidelines. High remission rates are observed in the setting of cytarabine- or anthracycline-based induction regimens. The CD33-targeted antibody-drug conjugate gemtuzumab ozogamicin (GO) is FDA-approved for use in newly-diagnosed CD33+ AML; a meta-analysis of 5 prospective randomized studies investigating intensive chemotherapy (IC) +/- GO demonstrated an improved overall survival (OS) with the addition of GO to IC for favorable-risk AML (Hills et al, Lancet Oncol 2014). The trials included in the meta-analysis did not restrict inclusion criteria to CBF-AML alone and there remains variation amongst IC regimens utilized in CBF-AML treatment. In addition, IC combined with the KIT inhibitor dasatinib has shown remission rates and promising overall survival in prospective studies (Paschka et al, Leukemia 2018; Marcucci et al, Blood Adv 2020). We set out to investigate the outcomes of patients (pts) with CBF-AML treated with IC +/- targeted agents (GO or KIT inhibitor) across 5 institutions that are part of the Consortium on Myeloid Malignancies and Neoplastic Diseases (COMMAND).

Methods: Retrospective chart review was done to identify pts who were treated with IC with AML harboring inv(16)/t(16;16) or t(8;21) identified on cytogenetics, from January 2010 through April 2023, and were treated across 5 geographically-diverse academic institutions. Pt clinical characteristics, cytogenetics, molecular mutations, treatment, relapse, and OS data were collected. Relapse-free survival (RFS) and OS were both analyzed using Kaplan-Meier analysis.

Results: One-hundred forty-nine consecutive pts with CBF-AML were identified, 76 (51%) with inv(16) and 73 (49%) with t(8;21). Median age of pts was 47 years (yrs) (range 18-80yrs), with 64% male pts, and 106 (71%) pts had an ECOG performance status of 0-1. One-hundred seven (72%) pts identified as non-Hispanic White, 22 (15%) identified as non-Hispanic Black, and 12 (8%) identified as Hispanic. Molecular testing via next-generation sequencing was available for 124 pts (83%); 49 (33%) pts had adverse-risk ELN cytogenetics or mutations when excluding CBF status, and 27 (18%) pts harbored KIT mutations. Other baseline pt characteristics are listed in Table 1A.

All pts underwent induction with IC; 44 (30%) pts received IC + GO, 21 (14%) received IC + KIT inhibitor (14 received dasatinib, 7 received midostaurin), and the remaining 84 (56%) received IC without a targeted agent. One-hundred fourteen (77%) pts achieved a complete response (CR) to induction therapy, and 1 pt experienced induction-related mortality. Fluorescence in-situ hybridization (FISH) data was available in 82 pts at end of induction with 83% achieving FISH negativity. Measurable residual disease (MRD) testing was done by polymerase chain reaction (PCR) in 62 pts with 76% achieving MRD-negativity.

One-hundred forty pts underwent consolidation with a median of 3 cycles of chemotherapy; 21 (15%) pts received GO with consolidation and 17 (12%) received a KIT inhibitor with consolidation. Forty-four (30%) pts underwent allogeneic stem cell transplantation (alloSCT), with 17 in first CR, and 27 after second-line or beyond therapy.

With a median follow-up of 22.5 months, the observed 3-yr RFS was 51% (95% CI: 43-61%) and the 3-yr OS was 69% (95% CI: 61-78%). Pts treated with IC + KIT inhibitor had significantly improved 3-yr RFS of 85% (95% CI: 70-100%) compared to other pts, including those who received IC + GO who had a 3-yr RFS of 51% (95% CI: 37-70%) and those who received IC without targeted therapy who had a 3-yr RFS of 45% (95% CI: 35-58%) (p = 0.02) (Figure 1). Full survival statistics are shown in Table 1B and Figure 1.

Conclusions: In this multi-center retrospective study of pts with CBF-AML undergoing induction with IC regimens with diverse national treatment practices, we find that the addition of GO to IC is not associated with improved outcomes. Pts treated with IC + KIT inhibitor had significantly improved RFS; of note, pts receiving a KIT inhibitor oftentimes continued on maintenance even after consolidation. These data suggest that there may be a role for targeted therapies other than GO to be explored in randomized prospective studies of intensive induction chemotherapy for CBF-AML.