Why Is Actinium Pharmaceuticals Stock Rising Today?

• The company’s latest research shows ATNM-400 achieving substantial tumor-growth suppression.
• The therapy targets a validated antigen overexpressed in breast cancer and other solid tumors, such as Prostate Cancer and Non-Small Cell Lung Cancer.
• Researchers observed that ATNM-400 induced irreversible DNA damage.

Actinium Pharmaceuticals, Inc. (ATNM) stock was in the spotlight on Friday after the company announced promising new preclinical findings for its novel radiotherapy, ATNM-400, at the 2025 San Antonio Breast Cancer Symposium (SABCS). 

The Actinium-225 (Ac-225) antibody radioconjugate demonstrated strong anti-tumor activity across multiple breast cancer models, including hormone receptor–positive (HR+), triple-negative (TNBC), and treatment-resistant tumors.

ATNM-400’s Broad Potential

The company’s latest research shows ATNM-400 achieving substantial tumor-growth suppression with minimal side effects in preclinical studies. 

The therapy targets a validated antigen overexpressed in breast cancer and other solid tumors, such as Prostate Cancer and Non-Small Cell Lung Cancer (NSCLC), positioning ATNM-400 as a potential pan-tumor radiotherapy solution.

Following the update, Actinium’s stock traded over 3% higher in Friday’s premarket. On Stocktwits, retail sentiment around the stock remained in ‘neutral’ territory amid ‘normal’ message volume levels. 

Effectiveness Against Resistant Cancer Types

ATNM-400 displayed potent cytotoxic effects in models resistant to standard-of-care treatments, including trastuzumab-resistant BT474-Clone5 and tamoxifen-resistant MCF7-Tam1 cells. Combining ATNM-400 with conventional therapies like trastuzumab or tamoxifen enhanced tumor regression in preclinical models.

"Patients whose tumors progress after endocrine therapy or HER2-targeted therapies face limited and often toxic treatment options. The data presented at SABCS show that ATNM-400 generates potent, targeted DNA damage even in highly resistant breast cancer models, while maintaining a favorable tolerability profile,” said Aditya Bardia, Program Director, Breast Medical Oncology at Geffen School of Medicine, University of California, Los Angeles.

Researchers observed that ATNM-400 induced irreversible DNA damage, marked by elevated phosphorylation of H2AX (pH2AX) and AKT (pAKT), consistent with alpha-particle–driven double-strand DNA breaks. 

ATNM stock has gained over 17% year-to-date.

Also See: Nvidia Weighs Boosting H200 AI Chip Production: Report

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