Investing.com -- Actinium Pharmaceuticals Inc (NYSE:ATNM) stock rose 3.7% on Friday following the presentation of new preclinical data for its breast cancer therapy candidate ATNM-400 at the 2025 San Antonio Breast Cancer Symposium.
The company’s Actinium-225 based antibody radioconjugate demonstrated robust anti-tumor activity across multiple breast cancer models, including hormone receptor-positive, triple-negative, and treatment-resistant tumors. The therapy targets an antigen that is overexpressed in breast cancer cells, particularly those resistant to standard treatments like tamoxifen and trastuzumab.
ATNM-400 showed significant tumor growth inhibition in preclinical models while maintaining a favorable tolerability profile. The data revealed that the therapy’s Actinium-225 alpha-emitter payload induced irreversible double-strand DNA breaks, potentially producing localized tumor killing with reduced off-target toxicity compared to antibody drug conjugates.
The company is positioning ATNM-400 as a potential pan-tumor targeted radiotherapy that could address multiple breast cancer subtypes with limited treatment options. Beyond breast cancer, Actinium has previously presented data supporting the therapy’s potential in prostate cancer and non-small cell lung cancer.
Breast cancer remains the most diagnosed cancer among women in the United States, with approximately 316,950 women expected to be diagnosed in 2025. Hormone receptor-positive, HER2-negative breast cancer accounts for 70-75% of cases, representing the largest subtype.
Actinium Pharmaceuticals is developing ATNM-400 as both a monotherapy and in combination with existing treatments, with plans to advance the candidate toward clinical readiness.
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