Acute myeloid leukaemia (AML) is a rare blood cancer, accounting for approximately 1% of cancers globally. Despite recent advancements in AML treatment, the outlook for patients with relapsed or refractory (R/R) AML remains unfavourable. Allogeneic haematopoietic stem cell transplantation (HSCT) is the only potentially curative option for these patients. However, only a small portion of them achieve complete remission (CR) or sufficient disease control to undergo HSCT. Additionally, the older population tends to have poor tolerance to induction and conditioning regimens. Addressing this unmet need, Actinium Pharmaceuticals’s Iomab-B (¹³¹I-apamistamab) is an anti-CD45 radioimmunoconjugate that delivers targeted myeloablative radioactivity to stem cells and leukaemic blasts, thus reducing HSCT conditioning intensity.

At the European Hematology Association (EHA) conference during 8-11 June 2023, results were presented from the pivotal SIERRA Phase III study comparing the efficacy of Iomab-B-based HSCT conditioning versus physicians’ choice of care in older (55+ years), R/R AML patients usually ineligible for HSCT. These patients were randomly divided into two groups: one received Iomab-B followed by HSCT while the other received conventional care (CC) chosen by the physician. CC patients who achieved CR received physician’s choice conditioning and HSCT; CC patients not achieving CR could cross over to the Iomab-B group. Iomab-B demonstrated a twofold increase in one-year survival rates; among the patients not included in the crossover group, 26.1% remained alive compared to 13.1% in the control arm. Patients in the Iomab-B cohort displayed significantly longer median overall survival than those who received standard chemotherapy (6.4 months versus 3.2 months). Furthermore, the trial demonstrated that Iomab-B successfully achieved the primary objective of CR after HSCT for a duration of six months in 22% of patients compared to 0% in the control arm, with highly significant statistical results (p-value < 0.0001).

The promising outcomes from the SIERRA trial will contribute to establishing Iomab-B as the new standard treatment for R/R AML patients who were not traditionally considered candidates for HSCT. The absence of existing or apparent competitors for Iomab-B, along with the availability of specialised bone marrow transplantation centres, suggests that effective commercialisation of this valuable treatment is attainable, and GlobalData’s Consensus Forecast database projects global peak sales for Iomab-B to reach $81m by 2029. If approved by the FDA and EMA, with plans to launch a biologics licence application (BLA) in the second half of 2023, Iomab-B has the potential to become an inaugural targeted radiotherapy for conditioning before HSCT in patients with R/R AML.