A New Frontier: Magnetic Nanoparticle Hyperthermia for Solid Tumors

In November 2025, Mayo Clinic in Rochester, Minnesota installed the first magnetic nanoparticle hyperthermia system in the United States for cancer research. The first patient was treated in December 2025, marking a major step toward bringing a long‑overlooked concept into the modern, heavily pretreated cancer landscape.

Hyperthermia, the therapeutic use of heat, has been studied for decades. Raising tumor temperatures to roughly 40–50 °C can directly damage cancer cells and make them more sensitive to radiation and chemotherapy. However, traditional methods such as ultrasound‑heated water bags or microwave applicators struggled to heat deep tumors without burning the skin or causing severe discomfort. Techniques were often unreliable, painful, and difficult to integrate into routine oncology practice, so hyperthermia largely faded from mainstream use.

The new system at Mayo Clinic approaches the problem differently. Instead of heating tissue from the outside in, it uses intravenous nanoparticles that act as microscopic “heaters” only inside the tumor. Patients receive an infusion of specially engineered iron‑oxide nanoparticles that circulate through the bloodstream and accumulate in tumors, thanks to their leaky, abnormal blood vessels. After allowing time for the nanoparticles to concentrate, the patient is positioned inside an electromagnetic induction device that generates a rapidly alternating magnetic field around the torso.

The magnetic field passes through normal tissue without much effect, but when it encounters the iron‑oxide particles concentrated in the tumor, they convert that energy into heat. The tumor becomes the “pan” on an invisible induction cooktop, while most surrounding tissue remains relatively cool. To protect the patient, cooling blankets are applied and core and skin temperatures are monitored continuously. The nanoparticles themselves are designed so that the temperature they produce self‑limits at about 50 °C, helping to avoid uncontrolled overheating.

Mayo Clinic is currently enrolling patients with metastatic solid tumors in essentially any body site except the brain, as long as the lesions are within the torso and covered by the device. The trial focuses on individuals whose cancers have resisted multiple lines of treatment, including chemotherapy, targeted therapy, immunotherapy, and sometimes radiation. The primary goals are to assess safety, see whether the treatment can reliably heat tumors without causing unacceptable side effects, and gather early signals about whether it can slow disease progression or improve symptoms.

First‑in‑human data from related early‑phase work show that two patients with advanced liver cancer achieved stable disease after receiving the nanoparticles plus a short session of magnetic field exposure, with no significant systemic toxicity reported. MRI confirmed that the nanoparticles accumulated in the tumors and were gradually cleared from the liver and spleen over time. While these results are preliminary and based on very few patients, they support the idea that the technology can be used safely and that controlled heating of deep tumors is feasible.

One of the most attractive aspects of this approach is its potential to treat multiple metastases at once. Since the nanoparticles circulate through the bloodstream, they can reach several tumor deposits in different locations, as long as they fall within the magnetic field. This contrasts with local ablation techniques, such as radiofrequency or microwave ablation, which typically treat one lesion at a time and are limited to smaller, more accessible tumors.

Clinical trial.