With four FDA-approved oncology indications and trials exploring new uses, tumor treating fields are emerging as a promising therapeutic option for certain patients with cancer.

While using alternating electric fields to treat cancer may sound “far-fetched,” the growing body of evidence on tumor treating fields is “really exciting,” according to Helen Shih, MD, a radiation oncologist at Massachusetts General Hospital in Boston.

The therapy has been shown to improve survival outcomes in several late-stage or aggressive cancer settings and received its first FDA-approved indication 14 years ago for recurrent glioblastoma. Since then, the agency has added three more indications — one in 2015 for patients with newly diagnosed glioblastoma; another in 2019 for patients with unresectable, locally advanced, or metastatic malignant pleural mesothelioma; and most recently, a 2024 approval for metastatic non-small cell lung cancer (NSCLC).

Outside of these approved indications, researchers are investigating tumor treating fields to treat a range of other tumor types, including pancreatic and ovarian cancers as well as brain metastases from NSCLC.

Still, adoption of tumor treating fields has been limited. That’s in large part because the treatment is time intensive and can affect patients’ quality of life.

Here’s a look at how it works, the body of evidence, and the limitations.

What Are Tumor Treating Fields?

Tumor treating fields use low intensity, alternating electric fields to disrupt cancer cell division.

The electric fields are generated by a wearable device — Optune Gio for glioblastoma and Optune Lua for pleural mesothelioma and NSCLC — developed and marketed by Switzerland-based oncology company Novocure.

The device consists of a portable generator and adhesive array patches — also called transducer array patches — which patients wear on the skin near the tumor site. These patches deliver the electric fields, typically at frequencies between 100 kHz and 300 kHz. The specific frequency depends on the cancer type. For glioblastoma, about 200 kHz is the optimal frequency for disrupting cell division, while that frequency is about 150 kHz for mesothelioma.

Patients receive continuous treatment for about 18 hours a day, and patches are replaced every few days to maintain good contact and reduce skin irritation.

The list price is roughly $21,000 per month, which is comparable to many oncology drugs, and covers a range of costs, including equipment rental and replacement arrays.

The Approval Landscape

The FDA first approved tumor treating fields to treat recurrent glioblastoma in 2011. The approval was based on the EF‑11 trial, which randomized 237 patients with recurrent glioblastoma to either tumor treating fields (200 kHz) or physician’s choice of chemotherapy. The trial did not show an overall survival advantage among patients receiving tumor treating fields — the 1-year overall survival rate was 20% in both groups — but did demonstrate a slightly higher progression-free survival rate at 6 months (21.4% vs 15.1%; P = .13) and improved toxicities and quality-of-life.

The second glioblastoma approval occurred in 2015, following results from the EF-14 trial. Among 695 patients with newly diagnosed glioblastoma, median overall survival was 20.9 months among those who received tumor treating fields (200 kHz) plus temozolomide vs 16.0 months among those who received temozolomide-alone (hazard ratio, 0.63; P < .001). The 2-year overall survival rate was 43% in tumor treating fields group vs 31% in temozolomide group.

A 2019 approval, which occurred via a Humanitarian Device Exemption, was based on the single-arm STELLAR trial in 80 patients with unresectable, locally advanced, or metastatic malignant pleural mesothelioma who received tumor treating fields (150 kHz) plus pemetrexed‑platinum chemotherapy. Median overall survival was 18.2 months compared with 12.7 months based on previous data in patients receiving chemotherapy alone.

Finally, in 2024, the FDA approved tumor treating fields for patients with metastatic NSCLC who had progressed on platinum-based chemotherapy. In the LUNAR trial, 276 patients were randomized equally to tumor treating fields (150 kHz) in combination with standard PD-1/PD-L1 inhibitors or docetaxel or to standard therapy alone. Patients in the tumor treating fields group had a 3.3-month median overall survival benefit — 13.2 months vs 9.9 months — but the benefit was greatest in patients who received immune checkpoint inhibitors — 18.5 months vs 10.8 months.

The company also recently filed a premarket approval application to the FDA for unresectable locally advanced pancreatic cancer, based on findings from the PANOVA-3 trial presented at this year’s American Society of Clinical Oncology (ASCO) annual meeting.

Researchers reported a small but significant median overall survival benefit of 2 months in patients who received tumor treating fields alongside gemcitabine and nab-paclitaxel as well as a significantly better 1-year survival rate — 68.1% vs 60.2%. Patients receiving tumor treating fields also experienced a pain-free survival benefit — median 15.2 vs 9.1 months — and a 1-year pain-free survival rate of 54.1% vs 45.1%.

“The combination of survival increase and quality of life benefits suggests that this could be an approach we could use in patients with locally advanced pancreatic cancer,” ASCO study discussant Brian Wolpin, MD, a gastrointestinal medical oncologist at Dana Farber in Boston, said during the presentation.

Why Such Limited Use?

Despite the approved indications, adoption of tumor treating fields has been limited.

As of late September 2025, Novocure reported 4416 active users worldwide, including 4277 patients with glioblastoma, 100 with metastatic NSCLC, and 39 with mesothelioma. Shih estimates that only about 10% of eligible US patients with glioblastoma are offered tumor treating fields but this would vary by center.

A major issue, Shih said, is that “the quality-of-life impact on these patients is no joke.”

For glioblastoma, patients must keep their head shaved and wear four transducer patches that almost entirely cover the scalp. The patches are connected by cables to a 2.7-lb field generator that can be plugged in or carried in a bag or backpack with rechargeable batteries. The ceramic transducers cannot get wet, so patches must be removed for showers.

For mesothelioma and NSCLC, patients wear four large arrays on the upper torso. Skin reactions can occur in more than half the patients, ranging from mild redness and rash to moderate blistering or ulceration. When severe enough, skin reactions may require a break in treatment.

Patients may find the therapy difficult to complete. In the PANOVA-3 trial, 8.4% of patients had device-related adverse events that led to treatment discontinuation. In another recent report, 40 patients with glioblastoma highlighted the pros and cons of tumor treating fields. Patients who chose the therapy noted downsides, including the burden of changing the arrays, which could be painful, as well as skin reactions, such as blisters or itching, and difficulty sleeping or carrying the device. For those who declined the therapy, the main reasons included head shaving, appearing sick, and the hassle of dealing with the equipment.

“There’s a lot of literal baggage going on,” Shih said. “You’ve got your transducer. You have wires. You have power packs. You have to carry your batteries and your charger.”

Shih acknowledges the challenges of this treatment but hopes the burdens can eventually be overcome. “We need to be open-minded,” Shih said.

Shih and Wolpin had no financial ties to Novocure.

M. Alexander Otto is a physician assistant with a master’s degree in medical science and a journalism degree from Newhouse. He is an award-winning medical journalist who worked for several major news outlets before joining Medscape. Alex is also an MIT Knight Science Journalism fellow. Email: aotto@mdedge.com.