131I-Apamistamab Prior to HSCT Demonstrates Favorable Safety Profile in AML

By Leah Sherwood - June 26, 2023

Conditioning with 131I-apamistamab (iomab-B) followed by allogeneic hematopoietic stem cell transplant (HSCT) resulted in statistically significant improvement in durable complete remission (dCR) at six months and a favorable safety profile in patients with relapsed or refractory acute myeloid leukemia (AML), according to recent research.

The research was presented at the SNMMI 2023 Annual Meeting by Neeta Pandit-Taskar, MD, of Memorial Sloan Kettering Cancer Center, and colleagues.

The data were from the SIERRA randomized controlled phase III study comparing the rate of dCR at six months between targeted high-dose radiation delivery of 131I-apamistamab, a radioimmunoconjugate to CD45, as an induction and conditioning regimen followed by HSCT versus physician’s choice of conventional care.

Patients 55 years or older with active relapsed or refractory AML were randomized (1:1) to Iomab-B or conventional care arms. Patients on 131I-apamistamab arm received 131I-apamistamab with fludarabine and total body irradiation (2 Gy) followed by HSCT. Patients on the conventional care arm received the physician’s choice of salvage therapy. Patients on the conventional care arm achieving CR received physician’s choice conditioning and HSCT, and those that did not were eligible to cross over to the 131I-apamistamab arm.

The SIERRA trial enrolled 153 patients, 76 in the 131I-apamistamab arm and 77 in the conventional care arm. All patients who received the therapeutic dose of 131I-apamistamab (n=66) underwent HSCT versus 14 (18.2%) on the conventional care arm, with 44 patients in the conventional care arm crossing over to the 131I-apamistamab arm and 40 receiving the therapeutic dose.

The primary endpoint of dCR at six months strongly favored 131I-apamistamab with 22% dCR versus 0% for conventional care (P<.0001) and event-free survival (EFS) at six months was 26% versus 0.2% for 131I-apamistamab versus conventional care (P<.0001). 131I-apamistamab followed by HSCT was well tolerated with lower rates of sepsis for 131I-apamistamab versus conventional care (6.1% vs. 28.6%), and 43.9% versus 50% febrile neutropenia and 15.2% versus 21.4% mucositis, respectively.

“Iomab-B based conditioning followed by [HSCT] resulted in statistically significant improvement in dCR at [six] months and a favorable safety profile,” the authors wrote. “Treatment with Iomab-B was able to safely deliver high doses of targeted radiation to leukemic cells, highlighted by the doses to spleen and bone marrow, with successful marrow engraftment, far outweighing what would be safely deliverable using total body irradiation.”


Pandit-Tasker N, Natwa M, Chen MK, et al. Individualized dosing for high-dose targeted radiation of hematopoietic cells with Iomab-B (I131-apamistamab) prior to HCT in relapsed/refractory acute myeloid leukemia (R/R AML): safety and efficacy results from the pivotal phase 3 SIERRA trial. Abstract #P685. Presented at Society of Nuclear Medicine and Molecular Imaging 2023 Annual Meeting; Chicago, Illinois, June 24-27.

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