On Aug. 1, 2025, the Mayo Clinic announced it had treated the first person in the U.S. using a novel radioactive medicine for advanced breast cancer as part of an international multisite clinical trial.

The medicine used in this clinical trial contains actinium-225, a highly potent alpha-emitting radiopharmaceutical therapy that was first developed for a subtype of gastroenteropancreatic neuroendocrine tumors, which are rare and can form in the pancreas and the gastrointestinal tract. The alpha-emitting radiopharmaceutical therapy is intended to work by passing through the blood to stick to cancer cells, delivering powerful and precise radiation without harming healthy cells.

The Mayo Clinic researchers are the first to apply this therapy in America to a patient with metastatic breast cancer. The phase 1b/2 open-label trial is being conducted at all three academic Mayo Clinic sites in Rochester, Minnesota; Phoenix; Jacksonville, Florida; and approximately 20 other sites across the U.S. The first person treated was at Mayo Clinic in Florida.

Mayo Clinic has nearly 20 active radiopharmaceutical therapy clinical trials, with 10 more preparing to launch, targeting many different types of cancer. Mayo Clinic in Rochester treats more patients with modern radiopharmaceutical therapies, such as lutetium dotatate for neuroendocrine cancers and lutetium PSMA for prostate cancers, than any other center in the world.

In preclinical studies, data indicates actinium-225 DOTATATE that targets the somatostatin receptor subtype 2expression demonstrated feasibility and potential efficacy for treatment of ER+ metastatic breast cancer in the laboratory. The drug was developed by RayzeBio, a Bristol Myers Squibb Company, the sponsor of the active phase 1b/2 clinical trial.