Iomab-B in combination with reduced-intensity conditioning (RIC) enables allogeneic hematopoietic stem cell transplant (ASCT) in a population of patients who are not typically eligible for transplant, according to a presentation at the 2023 Tandem Meetings.
Researchers evaluated Iomab-B (131I-apamistamab) plus RIC, followed by ASCT, in patients with relapsed or refractory acute myeloid leukemia (AML) who were 55 years of age or older.
All patients in the Iomab-B arm achieved engraftment, 75% achieved a complete response (CR) or CR without platelet recovery (CRp), and 60% of patients who achieved a durable CR were still alive at 2 years.
The researchers compared Iomab-B plus RIC to physician’s choice of conventional care, followed by ASCT, in the phase 3 SIERRA trial (ClinicalTrials.gov Identifier: NCT02665065). The trial included 153 patients with active, relapsed/refractory AML who were 55 years of age and older.
Patients were randomly assigned to receive Iomab-B plus RIC with fludarabine and total body irradiation (n=76) or conventional care (n=77), each followed by graft-vs-host disease (GVHD) prophylaxis and ASCT. Baseline characteristics were generally well balanced between the arms.
All 66 patients who received a therapeutic dose of Iomab-B underwent ASCT. In the conventional care arm, 62 patients did not achieve a CR, 44 of these patients crossed over to the Iomab-B arm, and 40 underwent ASCT. There were 14 patients in the conventional care arm who achieved a CR without crossing over to the Iomab-B arm, and all 14 underwent ASCT.
The per-protocol population included 59 patients in the Iomab-B arm and 64 in the conventional care arm. The rate of CR/CRp was 74.6% in the Iomab-B arm and 6.3% in the conventional care arm. Among patients who crossed over from conventional care to Iomab-B, the CR/CRp rate was 52.3%.
The rate of durable CR (lasting at least 180 days) was 22% in the Iomab-B arm and 0% in the conventional care arm (P <.0001). Among patients who crossed over from conventional care to Iomab-B, the durable CR rate was 13.6%.
The 6-month event-free survival rate was 28% in the Iomab-B arm 0.2% in the conventional care arm (hazard ratio, 0.22; 95% CI, 0.15-0.34; P <.0001).
The median overall survival (OS) was 6.4 months in the Iomab-B arm, 3.2 months in the conventional care arm without crossover, and 7.1 months in the crossover cohort. The 1-year OS rate was 26.0%, 13.1%, and 35.8%, respectively.
Among patients in the Iomab-B arm who achieved a durable CR, the 6-month OS rate was 100%, the 12-month OS rate was 92.3%, and the 24-month OS rate was 59.9%.
The rate of grade 3 or higher febrile neutropenia was 43.9% in the Iomab-B arm and 50.0% in the conventional care arm. Sepsis occurred in 6.1% and 28.6% of patients, respectively. Mucositis occurred in 15.2% and 21.4%, respectively. Grade 3-4 acute GVHD occurred in 9.4% and 14.3%, respectively.
Disclosures: This research was supported by Actinium Pharmaceuticals. The study authors declared affiliations with Actinium and many other companies.
Gyurkocza B, Choe H, Abboud C, et al. Efficacy and safety results of the SIERRA trial: A multicenter, pivotal phase 3 study of Iomab-B prior to allogeneic hematopoietic cell transplantation versus conventional care in older patients with active, relapsed or refractory acute myeloid leukemia (R/R AML). Tandem Meetings 2023. February 15-19, 2023. Abstract LBA3.