AML-287

Rapid Reduction of Peripheral Blasts in Older Patients with Refractory Acute Myeloid Leukemia (AML) Using Re-Induction with Single Agent Anti-CD45 Targeted Iodine (131I) Apamistamab [Iomab-B] Radioimmunotherapy in the Phase III SIERRA Trial.

Rapid reduction of peripheral blasts in older patients with refractory acute myeloid leukemia (AML) using reinduction with single agent anti-CD45 targeted iodine (131I) apamistamab [Iomab-B] radioimmunotherapy in the phase III SIERRA trial.

Benjamin Tomlinson1, Vijay Reddy2, Mark S. Berger2, Jennifer Spross2, Renee Lichtenstein2, Boglarka Gyurkocza3

1 University Hospitals Case Medical Center, Cleveland, OH, 2Actinium Pharmaceuticals, New York, NY, 3 Memorial Sloan Kettering Cancer Center, New York, NY

Poster Number: AML-287

2019 SOHO Annual Meeting

September 11 – 14, 2019

Houston, Texas

The SIERRA trial is a prospective, randomized, phase 3, open-label, ongoing multicenter trial for patients aged ≥55 years with active, relapsed/refractory (R/R) AML evaluating allogeneic hematopoietic cell transplantation (HCT) versus conventional care (CC). Recent preliminary data demonstrated robust donor engraftment in all patients treated with Iomab-B (Agura et al, Blood 2018 132:1017) despite active disease.  Rapid peripheral blast clearance is predictive of CR and RFS after cytotoxic chemotherapy for AML (Elliot et al, Blood 2007 110:4172; Gianfaldoni et al, BJH 2006 134:54).  In the present study we characterize the anti-leukemic effect and rate of peripheral disease reduction by single-agent Iomab-B.

We hypothesize that successful engraftment following HCT may be related to myeloablation and anti-leukemic activity by single agent Iomab-B prior to RIC.

Patients are randomized to receive Iomab-B and HCT or to a CC therapy including approved targeted agents followed by HCT if in remission. Majority of patients (79%) in the CC arm did not achieve CR and the study allowed crossover to receive Iomab-B.

Data were evaluated for the first 25% of patients (N = 38).  29 patients received Iomab-B, either directly (N = 19) or via crossover (N = 10). Median baseline marrow blasts were 30% (4-74) for Iomab-B and 24% (6-70%) for CC, which increased to 45% (10-70%) at crossover. Peripheral blast data was available in 16 patients (Iomab-B 7, Crossover 9). By day 3 post-Iomab-B, blasts were reduced by 98% with 100% reduction by day 8 (assuming 0% blasts due to lack of differential at WBC 0.1).  All patients engrafted with ANC at a median of 13 days (9-22 days). Patients treated with hydroxyurea versus without were analyzed together as well as separately and showed similar results. One patient received hydroxyurea post-Iomab-B therapeutic infusion.