Actinium presents breast cancer data for ATNM-400 at medical conference

Actinium Pharmaceuticals Inc. (NYSE American: ATNM) presented preclinical data for its experimental cancer treatment ATNM-400 at the 2025 San Antonio Breast Cancer Symposium. The data showed activity against multiple breast cancer types, including hormone receptor-positive, triple-negative, and treatment-resistant forms.

The company reported that ATNM-400 demonstrated tumor growth inhibition in laboratory models of hormone receptor-positive and triple-negative breast cancer. The treatment also showed activity in models resistant to standard therapies tamoxifen and trastuzumab, according to the press release.

ATNM-400 is designed to deliver Actinium-225 alpha-particle radiation to cancer cells. The treatment targets an antigen that the company states is overexpressed in breast cancer and other solid tumors including prostate cancer and non-small cell lung cancer.

Dr. Aditya Bardia, Professor of Medicine at UCLA's Geffen School of Medicine and an author on the study, said the data show ATNM-400 generates targeted DNA damage in resistant breast cancer models while maintaining tolerability.

Breast cancer represents the most diagnosed cancer among women in the United States, with approximately 316,950 women expected to be diagnosed in 2025, according to the National Cancer Institute. The company noted that hormone receptor-positive, HER2-negative breast cancer accounts for 70-75% of breast cancer cases.

Sandesh Seth, Chairman and CEO of Actinium Pharmaceuticals, stated that the data support the company's plans to accelerate development of ATNM-400 toward clinical readiness. The treatment remains in preclinical development.

The research findings were based on a company press release statement.

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