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Gus Iversen, Editor in Chief | August 05, 2025
Mayo Clinic has treated the first patient in the United States with an investigational alpha-emitting radiopharmaceutical for metastatic breast cancer, as part of a phase 1b/2 international clinical trial.
The drug, 225Ac-DOTATATE (also known as RYZ101), contains actinium-225, a high-energy alpha particle emitter designed to target and destroy cancer cells with minimal damage to surrounding tissue. It was originally developed to treat gastroenteropancreatic neuroendocrine tumors but is now being tested for use in estrogen receptor-positive (ER+), HER2-negative breast cancers that express somatostatin receptors and have progressed after standard treatments.
Mayo Clinic’s Florida campus was the first U.S. site to administer the therapy, which is being evaluated across all three of Mayo’s academic locations in Rochester, Minnesota; Phoenix, Arizona; and Jacksonville, Florida. Roughly 20 other sites across the country are expected to participate in the ongoing trial, sponsored by RayzeBio Inc., a Bristol Myers Squibb company.
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“This means alpha emitters can deliver a much more powerful impact over a shorter distance,” said Dr. Geoffrey Johnson, principal investigator and professor of radiology at Mayo Clinic. “The alpha emitter's potential lies in its power and in its ability to precisely kill even a single cancer cell without injuring surrounding healthy tissue, making it a next-generation therapy.”
The trial, listed under the identifier NCT06590857, is also studying the drug in combination with pembrolizumab, a checkpoint inhibitor, in patients whose cancers have failed to respond to antibody-drug conjugates or chemotherapy.
Mayo Clinic currently has nearly 20 active radiopharmaceutical therapy trials underway, with 10 more in preparation. The institution reports treating more patients globally with lutetium-based therapies for neuroendocrine and prostate cancers than any other center.
Preclinical data suggested actinium-225 DOTATATE could be effective in targeting ER+ metastatic breast cancer cells that express somatostatin receptor subtype 2, supporting the rationale for clinical investigation.
