Actinium Pharma To Present Preclinical Data For ATNM-400, Actinium-225 Antibody Radioconjugate, In HR+, HER2+ And Triple-Negative Breast Cancer At SABCS 2025

•  Presentation to include new data in triple-negative disease, a breast cancer subtype with poor outcomes and limited viable treatment options
   
• ATNM-400 overcomes HER2 therapy resistance and represents a novel targeted radiotherapy with the potential to avoid off-target toxicities including ILD that constrains other therapeutic modalities such as antibody drug conjugates
   
• ATNM-400 has demonstrated the potential to overcome resistance to first-line tamoxifen endocrine therapy
   
• Data to be presented on December 11, 2025 at 5:00 PM CT

NEW YORK, Dec. 1, 2025 /PRNewswire/ -- Actinium Pharmaceuticals, Inc. (NYSE:ATNM), a leader in the development of differentiated targeted radiotherapies, today announced compelling preclinical data for ATNM-400, a first-in-class Actinium-225 (AC-225) antibody radioconjugate, in hormone receptor positive (HR+), HER2 positive (HER2+) and triple-negative breast cancer (TNBC) that will be presented at the San Antonio Breast Cancer Symposium (SABCS) being held December 10‑14, 2025 in San Antonio, Texas. The data demonstrates significant anti-tumor activity in breast cancer models resistant to standard-of-care therapies including endocrine therapy tamoxifen and HER2-targeted therapy trastuzumab (Herceptin, Roche) as well as potent tumor growth inhibition in TNBC models. The data highlight ATNM-400's potential to address critical unmet needs in patients who have exhausted treatment options following endocrine therapy or HER2-targeted therapy failure. These data add to ATNM-400's robust preclinical data package that also encompasses metastatic castrate-resistant prostate cancer (mCRPC) and non-small cell lung cancer (NSCLC).