Off-Label Use of Venetoclax Combination Therapy in Relapsed/Refractory Acute Myeloid Leukemia: A Single Institution Experience

Introduction

Venetoclax (VEN) is a selective BCL-2 inhibitor that has demonstrated activity against acute myeloid leukemia (AML) and has been shown to be effective when used in combination with hypomethylating agents (HMAs) or low-dose cytarabine (LDAC) for treatment-naïve, elderly AML patients unfit for intensive chemotherapy. Data on its use in the relapsed/refractory setting is limited.

Methods

A retrospective analysis was performed among 12 relapsed or refractory AML patients treated with VEN combination therapy at the University of California Los Angeles from 2018-2019. Seven patients received VEN in combination with azacitidine (75 mg/m² x 7 days), 4 patients with decitabine (20 mg/m² x 5 days), and 1 patient with low-dose cytarabine (20 mg/m² x 10 days).

Results

The median patient age at time of VEN therapy was 58 years (range 41-79). Four patients (33.3%) had secondary AML. The majority (9 patients, 75.0%) had adverse cytogenetics. Three patients (25.0%) had received an allogeneic stem cell transplant prior to VEN therapy, and 5 patients (41.7%) had failed HMA therapy prior. Notable molecular mutations present were TP53 (4 patients, 33.3%), FLT3 (3 patients, 25.0%), and IDH2 (1 patient, 8.3%). Eight patients (66.7%) had grade 3 or greater neutropenia at time of VEN initiation, and 9 patients (75.0%) had grade 3 or greater thrombocytopenia. Four patients (33.3%) had a grade 3 or greater infection prior to VEN therapy.

Dosing of VEN was by physician discretion with a median starting dose of 150 mg (range 100-800) and a median maintenance dose of 450 mg (range 200-800). The median number of cycles of VEN combination therapy was 2 (range 1-5). Seven patients (58.3%) had decreased VEN dosage due to concomitant azole for antifungal prophylaxis. Four patients (33.3%) were on an additional small molecular inhibitor while receiving VEN therapy (sorafenib in 3 patients, ruxolitinib in 1 patient). The majority (10 patients, 83.3%) had an interruption in VEN dosing for the following reasons: bone marrow functional delay (7 patients), inability to tolerate oral pills (4 patients), infection (3 patients), and bleeding (2 patients).

The objective response rate (ORR) was 41.7% with 3 patients (25.0%) achieving complete remission with incomplete hematologic recovery (CRi) and 2 patients (16.7%) achieving partial remission (PR) (Table 1). Three patients (25.0%) experienced early death within 30 days due to the following: pneumonia (1 patient), multi-organ failure from infection and graft-versus-host disease (1 patient), and intracranial hemorrhage (1 patient). The median time to first and best response was 56 days (range 27-101) or after approximately 2 cycles of VEN combination therapy.

During VEN therapy, all patients (100%) had grade 3 or greater neutropenia and thrombocytopenia, and 10 patients (83.3%) had grade 3 or greater anemia. The nadir of most cytopenias occurred during cycle 1. Six patients (50.0%) developed a grade 3 or greater infection following VEN therapy, and 2 patients (16.7%) developed a grade 3 or greater intracranial hemorrhage. The only other notable grade 3 or greater side effects noted during VEN therapy were dizziness (1 patient, 8.3%) and diarrhea (1 patient, 8.3%).

After a median follow-up time of 3.14 months (range 1.22-13.48), 2 patients (16.7%) progressed, and the 1-year progression-free survival (PFS) rate was 71.11% (95% CI 43.40-100.00) (Figure 1). Eight out of 12 patients died as a result of infection (6 patients, 50.0%), disease progression (1 patient, 8.3%), and bleeding (1 patient, 8.3%). The median overall survival (OS) was 4.74 months (range 1.18-9.15), and the 1-year OS rate was 14.60% (95% CI 2.54-83.80) (Figure 2). VEN was discontinued in all patients because of no response (5 patients, 41.7%), adverse effects (4 patients, 33.3%), transition to donor lymphocyte infusion (1 patient, 8.3%), or transition to allogeneic stem cell transplant (2 patients, 16.7%).

Conclusions

We present our institutional experience with VEN combination therapy for the treatment of relapsed/refractory AML with a particularly high-risk patient cohort, predominantly characterized by adverse genetic features and grade 3 cytopenias prior to start of therapy. Overall, the response rate was modest, but not inferior to that with conventional salvage chemotherapy. Adverse events were primarily due to pre-existing bone marrow failure, likely exacerbated by treatment.

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