Long-Term Follow-Up Shows Continued Efficacy of Iomab B-Led Allogeneic Hematopoietic Cell Transplantation in Older Patients With Active, R/R AML

In a long-term follow-up to SIERRA, a multicenter, randomized, controlled phase 3 study, researchers found that patients 55 years of age or older with active relapsed or refractory acute myeloid leukemia (R/R AML) who received ¹³¹I-apamistamab (Iomab B)-led allogeneic hematopoietic cell transplantation (alloHCT) had an improved durable complete response (dCR) compared with those who received conventional care. The findings were presented at the Society of Hematologic Oncology 2024 Annual Meeting in Houston, TX.

Older patients with R/R AML are generally ineligible for alloHCT due therapy intolerance. But Iomab B provides targeted radiation to CD45-expressing cells that limits off-target toxicity. In SIERRA, Iomab B-led alloHCT improved outcomes in older patients with active R/R AML. In the current study, Seropian and colleagues report on a subsequent analysis involving longer-term follow-up (as of January 2024).

They randomized patients 1:1 (n = 153) to conventional care or Iomab B with fludarabine and total body irradiation (2 Gy) followed by alloHCT (77 patients in the conventional care group; 76 patients in the Iomab B group). The primary endpoint was dCR, which the researchers defined as a remission lasting ≥180 days from initial complete response (CR) or complete remission with incomplete platelet recovery (CRp).

A total of 66 patients received a therapeutic dose of Iomab B and underwent alloHCT vs 14 patients in the conventional care group. Among the evaluable patients, 44 out of 59 patients treated with Iomab B achieved initial CR/CRp versus four patients in the conventional care group. Looking at the dCR rates, 22% of those in the Iomab B group achieved dCR vs 0% in the conventional care group. Median follow-up was 36.6 months and 43.6 months at primary and subsequent cutoffs.

The median overall survival was 6.3 months for the Iomab B group and 4 months for the conventional care group of patients at the January 2024 data cutoff. Of the patients who achieved dCR in the Iomab B group, 92.3% were alive at 1 year and 69.2% at 2 years. Additionally, the Iomab B group tolerated the therapy well. Indeed, they had lower sepsis and mucositis rates than standard patients treated with alloHCT.

“The primary endpoint of dCR was improved in patients greater than or equal to 55 years of age with active R/R AML receiving Iomab B-led alloHCT versus [conventional care],” Seropian and colleagues concluded. “Most patients achieving dCR are long-term survivors. Improved outcomes in Iomab-B-treated patients persisted at longer follow-up. The Iomab-B-led regimen was well-tolerated and provided access to potentially curative alloHCT in a patient population traditionally considered ineligible for transplant.”

Reference:
Seropian S, Gyurkocza B, Nath R, et al. Long-term follow-up demonstrates ongoing efficacy benefit of ¹³¹i-apamistamab-led allogeneic hematopoietic cell transplantation in older patients with active, r/r aml in the phase 3 sierra trial. In: Proceedings of the Society of Hematologic Oncology 2024 Annual Meeting. Clin Lymphoma Myeloma Leuk. 2024 Sept;9(24);Supplement 1:S302.