Mayo Clinic Begins US Trials of Magnetic Nanoparticle Heat Treatment for Cancer

Heat kills cancer cells. That principle has been known for over a century, and physicians have tried to exploit it in various forms - hot water bags pressed against chest walls, microwave antennas inserted into tumors, ultrasound beams focused through the body. Each approach hit practical limits: imprecise temperature control, inability to reach deep tumors, patient discomfort. A newly installed machine at Mayo Clinic in Rochester, Minnesota is testing whether iron oxide nanoparticles and electromagnetic induction can do the job more precisely than any predecessor.

The system, manufactured by Israeli company New Phase Ltd., became the first of its kind installed for cancer research in the United States when Mayo Clinic completed setup in November 2025. The first US patient received treatment in December 2025 as part of an ongoing clinical trial.

How the system works

The approach starts with an intravenous infusion of iron oxide magnetic nanoparticles. Because tumor vasculature is leaky and disorganized compared to normal tissue, nanoparticles tend to accumulate preferentially in solid tumors - a phenomenon known as the enhanced permeability and retention effect. Once the particles have collected in the tumor, the patient lies inside an electromagnetic induction device that generates alternating magnetic fields.

The physics is analogous to an induction stovetop. An induction cooktop does not heat its surface directly; it generates a fluctuating magnetic field that induces electrical currents in a compatible pan, heating the pan from within. In this system, the tumor loaded with iron oxide nanoparticles functions as the pan. The alternating magnetic field causes the nanoparticles to generate heat, raising the tumor temperature while surrounding normal tissue - which contains far fewer particles - heats much less.

A thermostatic coating on the nanoparticles limits maximum temperature to 50 degrees Celsius. Cooling blankets applied to the patient's body surface prevent systemic temperature from rising dangerously, and the clinical team monitors patients continuously throughout treatment.

"It works like an induction cooktop," said Scott Lester, M.D., a radiation oncologist at Mayo Clinic and co-principal investigator of the trial. "A special coating on the nanoparticles limits the temperature to no more than 50 degrees Celsius."

What the current trial is testing

The ongoing clinical trial enrolls patients with metastatic solid tumors - any location in the body except the brain - who have exhausted multiple lines of systemic therapy and other advanced treatments, including prior radiotherapy. The therapy can reach tumors deep within the body and can address multiple sites simultaneously.

"We are focusing on patients whose cancers are resistant to multiple lines of systemic therapies and other advanced treatments, including radiotherapy," said co-principal investigator Sean Park, M.D., Ph.D., radiation oncologist at Mayo Clinic Comprehensive Cancer Center.

The primary questions in this early study are safety and feasibility - whether the procedure can be administered without serious adverse effects and whether it produces measurable tumor heating. Efficacy data for a treatment that kills tumors will require larger, controlled trials.

The longer history of hyperthermia in oncology

The Mayo Clinic team has institutional memory with hyperthermia going back two decades. Radiation oncologists there previously used water-filled bags heated by ultrasound and placed on patients' skin - primarily on the chest walls of women with recurrent breast cancer after surgery and radiation. The technique showed occasional success but suffered from unreliable temperature control and patient discomfort, and fell out of favor. Broader studies of hyperthermia combined with radiation were also limited by the available technology.

"Now, we may have a more advanced method to reintroduce hyperthermia into cancer therapy," said Nadia Laack, M.D., chair of Radiation Oncology at Mayo Clinic.

Researchers plan to evaluate hyperthermia in combination with radiation therapy in future studies. The rationale is that heat sensitizes cancer cells to radiation damage - tumors that are radioresistant under normal conditions can become vulnerable when heated. If that effect holds in this system, it could allow effective treatment at lower radiation doses, reducing toxicity to surrounding healthy tissue.

What the evidence does not yet show

This is an investigational procedure at an early stage. The December 2025 patient was the first to receive this treatment in the United States, and the trial is actively enrolling. There are no published efficacy data from this system, and preclinical results with magnetic nanoparticle hyperthermia have been mixed depending on tumor type, particle distribution, and field parameters. The nanoparticle accumulation effect that makes the approach theoretically selective is also not perfectly consistent across patients or tumor types.

Mayo Clinic has disclosed a financial interest in the technology referenced in this work.