A New, Precisely Targeted Radiation Option Is Being Studied for Advanced Breast Cancer

Why this matters: Mayo Clinic has treated the first person in the United States with a new form of precisely targeted radiation for advanced breast cancer, delivered as a “smart” medicine that seeks out cancer cells. This was done within a multi-site clinical trial. Mayo Clinic News Network

What it is—in simple terms

This approach uses a tiny amount of radiation attached to a molecule that looks for specific targets on cancer cells. In other words, think of it as a smart courier that not only carries treatment straight to the tumor but also, at the same time, aims to limit exposure to healthy tissue. Ultimately, this dual focus makes the process both effective and safer for patients. In this study, the radiation source is actinium-225, a powerful “alpha” particle that delivers its energy over just a few cell widths, which is why researchers are excited about its precision. Mayo Clinic News Network

What exactly is being studied?

The trial (called TRACY-1) is testing an investigational medicine known as 225Ac-DOTATATE (RYZ101), alone or with pembrolizumab (immunotherapy). It’s designed for ER-positive, HER2-negative metastatic breast cancer that expresses somatostatin receptors (SSTRs) and has progressed after treatments like chemotherapy and/or antibody-drug conjugates. The study is active at all three Mayo Clinic sites and ~20 other U.S. centers. Mayo Clinic News Network

• Important: This therapy is only available in clinical trials right now. If you’re interested, talk with your oncologist about SSTR testing and whether a study site is appropriate for you. (See ClinicalTrials.gov listing NCT06590857 for details.) Mayo Clinic News Network

How is this different from older “radiopharmaceutical” treatments?

To begin with, you may hear about lutetium (Lu-177) therapies used in other cancers. Specifically, those are beta emitters. In contrast, Actinium-225 is an alpha emitter—much heavier and uniquely designed to release energy over a very short distance. Consequently, this difference highlights why researchers see it as a promising approach for targeted cancer treatment. Ultimately, the goal is to hit cancer cells hard while, at the same time, sparing nearby healthy tissue. Therefore, this balance explains why experts increasingly view it as a promising, next-generation option for treatment. Mayo Clinic News Network

A gentle call to action

• Ask your oncologist: “Does my tumor have somatostatin receptors (SSTRs) and should I have imaging or testing for this?”
• Discuss trials: “Am I a candidate for the TRACY-1 study or a similar clinical trial near me?”
• Learn more with support: Visit our Stage 4 Breast Cancer: Treatment Options (Comprehensive Guide) on Learn Look Locate for plain-language information and questions to bring to your next visit.
• Check official trial details: See NCT06590857 on ClinicalTrials.gov for participating locations and eligibility. Mayo Clinic News Network

“Targeted alpha therapy is a promising way to deliver powerful, ultra-focused radiation to cancer cells while limiting exposure to healthy tissues. For people with ER-positive metastatic breast cancer who have exhausted standard options, this research may open an important door. Clinical trials help us learn who benefits, how much, and how safely—and that’s how we move the field forward.”
– Ramji Rajendran, MD, PhD, Radiation Oncologist & Learn Look Locate Medical Advisor

Quick FAQs

Q1. Is this treatment available to everyone now?
A: Not yet. Currently, it’s still investigational and, therefore, available only in clinical trials, such as the ongoing TRACY-1 study. Mayo Clinic News Network

Q2. Who might qualify?
A: Specifically, people with ER+ / HER2- metastatic breast cancer whose tumors express SSTRs and who have progressed after certain treatments may qualify. Furthermore, eligibility may vary depending on the site’s specific criteria. Therefore, it’s important to consult your care team, who can help you check and confirm your options. Mayo Clinic News Network

Q3. Where is the trial running?
A: At Mayo Clinic (Rochester, Phoenix, Jacksonville) and ~20 additional U.S. sites. See the ClinicalTrials.gov page (NCT06590857) for updates. Mayo Clinic News Network