Phase III SIERRA trial of Iomab-B shows positive interim results in acute myeloid leukemia.- Actinium Pharma

Actinium Pharmaceuticals announced key interim findings from the pivotal Phase III SIERRA trial of Iomab-B, including feasibility and safety data, at 50% of total patient enrollment. The SIERRA trial (Study of Iomab-B in Elderly Relapse/Refractory Acute Myeloid Leukemia) is a 150-patient, 1:1 randomization Phase III pivotal trial that is studying Iomab-B (Iodine-131 apamistamab) compared to physician's choice of salvage chemotherapy in patients age 55 and above with active, relapsed or refractory AML (Acute Myeloid Leukemia). These interim data provide information on safety and feasibility of using Iomab-B to enable a BMT (Bone Marrow Transplant), the only curative treatment option in this patient population that is not typically considered eligible for BMT.

Patients enrolled in the SIERRA trial were a median age of 64 (55-76) and had active disease with a median bone marrow blast percentage at randomization of 28 percent (5-97%). All patients were intermediate or poor, adverse risk groups. Two-thirds (68%) of the patients enrolled were in the poor prognostic, adverse cytogenetic and molecular risk group. All patients receiving a therapeutic dose of Iomab-B (31/31) in the study arm received a bone marrow transplant and engrafted rapidly without delay in blood count recovery. Only 7/38 patients (18%) randomized to the control arm achieved an initial complete response (CR) and were able to proceed to a conventional bone marrow transplant. Of the 31 patients who failed the primary endpoint in the control arm (82% failure), 20 (64%) were considered eligible for potential rescue by treatment with Iomab-B followed by a BMT.

All 20 patients (100%) who crossed over and received a therapeutic dose of Iomab-B followed by a BMT achieved engraftment without delay in blood count recovery despite high blast count burden prior to transplant (median 35%). 12/38 patients (32%) randomized to the control arm received targeted agents all of which were recently approved. 11/12 patients (92%) received the Bcl-2 inhibitor venetoclax with either an hypomethylating agent or low dose cytarabine. Of these, only 3/11 patients (27%) achieved a CR. 100-day Non-Relapse Transplant Related Mortality remains lower in the Iomab-B arm (1/31 patients or 3%) compared to patients in the control arm who received conventional transplants (2/7 or 29%). Of the 31 patients who received Iomab-B in the study arm, 30 are potentially evaluable for the primary endpoint compared to 5 in the control arm. This difference between study arm and control arm remains consistent with that reported at the interim update at 25% of enrollment. The SIERRA trial remains the only randomized Phase III clinical trial to offer BMT as an option for patients age 55 and above with active, relapsed or refractory AML.