• Median Overall Survival of 5.49 months observed in patients with a TP53 mutation receiving an Iomab-B led allogeneic bone marrow transplant compared to 1.66 months in patients that did not receive Iomab-B (hazard ratio=0.23, p=0.0002) in the Phase 3 SIERRA Trial
• Long-term efficacy results in patients with active relapsed or refractory acute myeloid leukemia also observed in the SIERRA trial

NEW YORK, June 14, 2024 /PRNewswire/ -- Actinium Pharmaceuticals, Inc. (NYSE AMERICAN: ATNM) (Actinium or the Company), a leader in the development of Antibody Radiation Conjugates (ARCs) and other targeted radiotherapies, today announced that results from the Phase 3 SIERRA trial of Iomab-B were presented at the 2024 European Hematology Association (EHA) Hybrid Congress being held June 13 – 16, 2024, in Madrid, Spain. The two presentations at EHA highlighted outcomes in patients with active relapsed or refractory acute myeloid leukemia (r/r AML) enrolled in the SIERRA trial who had a TP53 mutation and long-term efficacy results in this older patient population.

The Phase 3 SIERRA trial enrolled 153 patients ages 55 and above with active r/r AML and compared outcomes of patients receiving an Iomab-B led bone marrow transplant (BMT) to those of patients receiving physician's choice of care in the control arm. Across all patients in SIERRA study, only patients receiving an Iomab-B led BMT achieved the trial's primary endpoint of durable complete remission with these patients having 92% 1-year survival and 69% 2-year survival with statistically significant higher event free survival. The SIERRA trial enrolled high-risk patients including those with one or more of the following: a TP53 mutation, advanced age up to 77 years old, complex cytogenetics and prior therapy including venetoclax and other targeted agents.

Highlights from Oral Presentation of Outcomes in Patients with a TP53 Mutation

-  In total, 24% (37/153) of the patients enrolled on SIERRA had a TP53 mutation, which is usually associated with limited treatment options and poor outcomes
-  For patients with TP53 mutation only those receiving Iomab-B (either at randomization or via cross-over) achieved complete remission or achieve a durable complete remission (dCR), the primary endpoint of the SIERRA trial
-  Median Overall Survival (OS) of 5.49 months observed in patients with a TP53 mutation receiving an Iomab-B led allogeneic bone marrow transplant compared to 1.66 months in patients that did not receive Iomab-B (hazard ratio=0.23, p=0.0002)
-  Median OS was 6.37 months in TP53 negative patients receiving Iomab-B and 5.72 months for TP53 positive patients demonstrating Iomab-B's ability to overcome TP53 gene mutations

Presentation Title: 131I-APAMISTAMAB-LED ALLOGENEIC HEMATOPOIETIC CELL TRANSPLANT RESULTS IN IMPROVED SURVIVAL OUTCOMES IN R/R AML PATIENTS WITH HIGH-RISK TP53 MUTATIONS IN THE RANDOMIZED PHASE III SIERRA TRIAL

Presenter: Dr. Hannah Choe, Assistant Professor of Medicine at Ohio State University and SIERRA trial investigator

Highlights from Presentation of Long-Term Efficacy Results

-  All patients receiving Iomab-B underwent a BMT compared to 18% on the control arm
-  75% of patients on the Iomab-B arm achieved a complete remission (CR) compared to 6.3% on the control arm
-  The durable complete remission (dCR) was 22% on the Iomab-B arm compared to 0% on the control arm. dCR is the primary endpoint of the SIERRA study and was met with high statistical significance with a p-value<0.0001
-  Of the patients achieving dCR after an Iomab-B led BMT, there was 92% 1-year survival and 69% 2-year survival with median overall survival not reached
-  Iomab-B was well tolerated with a favorable safety profile including lower rates of sepsis and mucositis in patients receiving an Iomab-B led BMT

Presentation Title: LONG TERM EFFICACY RESULTS OF THE SIERRA TRIAL: A PHASE 3 STUDY OF 131I-APAMISTAMAB-LED ALLOGENEIC HEMATOPOIETIC CELL TRANSPLANTATION VERSUS CONVENTIONAL CARE IN OLDER PATIENTS WITH ACTIVE, R/R AML

About Actinium Pharmaceuticals, Inc.

Actinium develops targeted radiotherapies to meaningfully improve survival for people who have failed existing oncology therapies. Advanced pipeline candidates Iomab-B (pre-BLA & MAA (EU)), an induction and conditioning agent prior to bone marrow transplant, and Actimab-A (National Cancer Institute CRADA pivotal development path), a therapeutic agent, have demonstrated potential to extend survival outcomes for people with relapsed and refractory acute myeloid leukemia. Actinium plans to advance Iomab-B for other blood cancers and next generation conditioning candidate Iomab-ACT to improve cell and gene therapy outcomes. Actinium holds more than 230 patents and patent applications including several patents related to the manufacture of the isotope Ac-225 in a cyclotron.

For more information, please visit: https://www.actiniumpharma.com/

Forward-Looking Statements

This press release may contain projections or other "forward-looking statements" within the meaning of the "safe-harbor" provisions of the private securities litigation reform act of 1995 regarding future events or the future financial performance of the Company which the Company undertakes no obligation to update. These statements are based on management's current expectations and are subject to risks and uncertainties that may cause actual results to differ materially from the anticipated or estimated future results, including the risks and uncertainties associated with preliminary study results varying from final results, estimates of potential markets for drugs under development, clinical trials, actions by the FDA and other governmental agencies, regulatory clearances, responses to regulatory matters, the market demand for and acceptance of Actinium's products and services, performance of clinical research organizations and other risks detailed from time to time in Actinium's filings with the Securities and Exchange Commission (the "SEC"), including without limitation its most recent annual report on form 10-K, subsequent quarterly reports on Forms 10-Q and Forms 8-K, each as amended and supplemented from time to time.

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