Novocure: Cancer Treatment Using Tumor Treating Fields

Tumor Treating Fields, or TTFields, are low-intensity alternating electric fields that interfere with cancer cell division, and the Israeli company Novocure has built an entire treatment platform around them. The device delivers electric fields through adhesive electrode arrays worn on the body near the tumor site, running continuously for as many hours per day as possible. What started as a controversial idea in neuro-oncology has now accumulated phase III trial data across glioblastoma, non-small cell lung cancer, mesothelioma, and most recently pancreatic cancer, with survival benefits that have shifted the treatment from curiosity to clinical standard in at least one disease.

How Electric Fields Disrupt Cancer Cells

TTFields work at the level of cell division. When a cell divides, it assembles a structure called the mitotic spindle from proteins including tubulin, which are highly electrically polar. The alternating electric fields exert forces on these polar molecules, scrambling the normal assembly of the spindle and disrupting the cleavage furrow that pinches a dividing cell into two daughter cells.¹ The result is abnormal division that leads to cell stress and death. Because cancer cells divide far more frequently than most healthy cells, TTFields disproportionately affect tumors while leaving slower-dividing normal tissue relatively unharmed.

The effect goes beyond just fouling up cell division. Research has shown that TTFields cause physical disruption of the nuclear envelope, releasing chunks of DNA called micronuclei into the cell’s interior. These stray DNA fragments trigger two major immune-sensing pathways, cGAS/STING and AIM2, which activate inflammatory signaling and type 1 interferons.² In plain terms, the electric fields don’t just kill cancer cells directly; they also generate an immune alarm that can help the body’s own defenses recognize and attack the tumor. This dual action, combining a direct anti-division effect with immune activation, is part of what makes TTFields appealing in combination with other therapies.

One quirk of TTFields is that the optimal frequency depends on cell size. Larger cells respond best to lower frequencies, while smaller cells need higher frequencies. This inverse relationship means that a single fixed frequency won’t hit every cancer cell in a tumor equally, and some cells may partially evade the treatment simply by being the wrong size for the chosen frequency.³ Novocure’s device uses 200 kHz for glioblastoma and 150 kHz for thoracic tumors, frequencies optimized for the typical cell sizes of those cancers.

The Glioblastoma Trial That Changed the Field

Glioblastoma is the most aggressive primary brain cancer in adults, and TTFields earned their clinical foothold here. The pivotal phase III trial, known as EF-14, randomized newly diagnosed glioblastoma patients to receive either the standard chemotherapy drug temozolomide alone or temozolomide plus TTFields. The results were striking: median overall survival reached about 21 months with TTFields added, compared to 16 months with chemotherapy alone. The five-year survival rate more than doubled, from roughly 5% to 13%.⁴ For a disease where almost no one survives five years, that shift was enough to change guidelines.

The story with recurrent glioblastoma, where the tumor comes back after initial treatment, is less impressive. An earlier trial tested TTFields as a standalone treatment in recurrent disease and found median survival of about 6.6 months with TTFields compared to 6.0 months with physician-choice chemotherapy, a difference that was not statistically meaningful. The one-year survival rate was around 20% in both groups.⁵ That trial did, however, demonstrate that TTFields were safe and feasible in a large multicenter setting, and it showed objective tumor responses in about 14% of patients compared to roughly 10% on chemotherapy. The upshot is that TTFields seem to matter most when added to chemotherapy in newly diagnosed patients, not as a rescue therapy after other treatments have failed.

Expanding Beyond the Brain

Novocure has been running trials in several cancer types outside the brain, and several have reported results.

Non-Small Cell Lung Cancer

The LUNAR trial tested TTFields added to standard systemic therapy in patients with metastatic non-small cell lung cancer that had already progressed on platinum-based chemotherapy. Median overall survival was about 13 months with TTFields plus standard treatment versus about 10 months with standard treatment alone, a statistically significant improvement. The treatment did not add systemic side effects beyond what standard therapy caused on its own.⁶ A cost-effectiveness analysis found that when TTFields were paired with an immune checkpoint inhibitor, the incremental cost was about $59,000 per quality-adjusted life year gained, a figure generally considered acceptable by conventional thresholds. Paired with the chemotherapy drug docetaxel, however, the cost per quality-adjusted life year jumped to over $300,000, reflecting a much smaller survival gain in that subgroup.⁷

Mesothelioma

Malignant pleural mesothelioma is a rare cancer of the lining of the lungs, notoriously difficult to treat when surgery is not an option. The STELLAR trial, a single-arm phase 2 study, treated 80 patients with TTFields at 150 kHz delivered to the chest alongside standard pemetrexed and platinum chemotherapy. Median overall survival was about 18 months, which compared favorably to historical expectations for this disease, and there was no increase in systemic toxicity.⁸ Without a randomized control group, the result is harder to interpret definitively, but it was encouraging enough to support device approval for mesothelioma in some regions.

Pancreatic Cancer

The most recent addition to the clinical pipeline is the PANOVA-3 trial in locally advanced pancreatic adenocarcinoma. This randomized phase III study compared TTFields plus gemcitabine and nab-paclitaxel against chemotherapy alone. Median overall survival was about 16 months in the TTFields group versus about 14 months with chemotherapy alone, a statistically significant difference.⁹ For a cancer where survival gains of even a few months have been rare, this result is noteworthy. It also extends the evidence for TTFields well beyond the brain, suggesting the mechanism has broader applicability to solid tumors.

What the Side Effects Actually Look Like

One of TTFields’ selling points is that the side effect profile is very different from chemotherapy or radiation. The treatment does not cause nausea, hair loss from drug toxicity, or immune suppression. The main issue is skin irritation under the electrode arrays, which sit against the body for days at a time. In the pivotal glioblastoma trial, about 16% of patients developed skin reactions, and post-marketing data from a larger group showed a somewhat higher rate of around 22%.¹⁰

The skin reactions range from mild contact dermatitis and itchiness to, more rarely, skin erosions, ulcers, or infection. Most are manageable. Prevention strategies include proper skin cleaning before applying the arrays and shifting the array position by a couple of centimeters each time the arrays are changed, which helps distribute the contact pressure. When reactions do happen, treatment depends on the type: topical corticosteroids for dermatitis, antibiotics for infections, moisturizers for dry skin. Water-based products are preferred over petroleum-based ones because petroleum increases the electrical impedance between the electrodes and the skin, reducing treatment effectiveness.¹¹

Living With the Device On Your Head

Wearing adhesive electrode arrays on a shaved scalp for 18 or more hours a day raises an obvious quality-of-life question. The secondary analysis of the EF-14 glioblastoma trial specifically tracked health-related quality of life across nine different scales over 12 months. On almost all measures, including physical functioning, social functioning, and cognitive status, there was no meaningful difference between patients using TTFields plus temozolomide and those on temozolomide alone.¹² The one exception was itchy skin, which was significantly worse in the TTFields group at 3, 6, and 9 months, though this difference disappeared by 12 months.

A separate analysis of the same trial population found that quality of life initially improved in the TTFields group compared to chemotherapy alone during the first six months, a difference that evened out by the nine-month mark. Karnofsky performance scores, a rough measure of a patient’s ability to carry out daily activities, stayed just below 90 in both groups. Cognitive screening scores were stable over time as well.¹³ The data suggest that the burden of wearing the device, while real and visible, does not translate into a measurable worsening of how patients feel or function overall. That said, clinical trial populations tend to be more motivated and better supported than average patients, so real-world adherence and experience may differ.

Could TTFields Help Drugs Reach the Brain?

One of the more intriguing findings from TTFields research has nothing to do with killing cancer cells directly. The blood-brain barrier, the tightly sealed network of blood vessels that keeps most drugs out of the brain, appears to become temporarily more permeable when TTFields are applied. In animal studies, compounds that normally cannot cross the barrier were found in healthy rat brains after TTFields exposure at 100 kHz. When brain-tumor-bearing rats received paclitaxel, a chemotherapy drug normally blocked by the barrier, in combination with TTFields, their tumors shrank more than with either treatment alone.¹⁴

Human 3D cell models have confirmed that the barrier disruption is reversible. After TTFields were stopped, barrier function started recovering within 24 hours and was fully restored within 48 hours.¹⁵ An imaging study in glioblastoma patients provided initial human evidence, showing increased blood-brain barrier permeability and blood volume in tumor regions in patients receiving TTFields with chemotherapy compared to chemotherapy alone.¹⁶ If this pans out clinically, it could mean that TTFields serve a dual purpose in brain cancers: directly fighting the tumor while also helping other drugs get through the barrier to reach it.

Combining TTFields With Radiation

Radiation therapy is already a standard part of glioblastoma treatment, and laboratory evidence suggests TTFields could make cancer cells more sensitive to radiation. The proposed mechanism involves DNA repair: after radiation damages a cancer cell’s DNA, the cell attempts to fix itself through a process called homologous recombination. TTFields appear to interfere with this repair pathway, leaving radiation-damaged cells less able to recover.¹⁷ Clinical trials testing TTFields alongside radiation are ongoing, but the preclinical rationale is strong enough that the combination is actively being pursued.

When Tumors Learn to Ignore the Fields

Like most cancer treatments, TTFields face the problem of resistance. Some tumors eventually stop responding, and researchers are beginning to understand why. In glioblastoma, prolonged exposure to TTFields has been linked to upregulation of a signaling axis involving the genes PTGER3 and ZNF488. This pathway promotes the self-renewal of glioblastoma stem cells, the subpopulation most responsible for tumor regrowth. The same genes were found to be upregulated after TTFields exposure across several other cancer cell types, from bladder to pancreatic to breast cancer, suggesting the resistance mechanism may be shared.¹⁸

In colorectal cancer cells, a different gene called NAALADL1 has been identified as a resistance factor. When researchers knocked down NAALADL1, cells became sensitive to TTFields again, and their microtubules became less stable, which amplified the electric fields’ disruptive effect on cell division. Virtual drug screening even identified two existing compounds, lumacaftor and bestatin, that inhibited NAALADL1 and worked together with TTFields to suppress cancer cell growth in the lab.¹⁹ These findings are still preclinical, but they point toward a future where resistance markers could guide patient selection or where existing drugs might be repurposed to restore TTFields sensitivity.

Personalizing Where the Electrodes Go

The placement of electrode arrays on the body matters more than you might expect. The electric field does not distribute evenly through tissue; it bends and concentrates differently depending on the anatomy between the electrodes and the tumor, including skull thickness, tissue composition, and tumor location. Computational modeling using patient MRI scans can simulate how the field distributes through an individual patient’s anatomy, and optimizing electrode placement based on those simulations can increase the field intensity at the tumor by more than 31% compared to standard positioning.²⁰

Research groups have developed semi-automated workflows that take a patient’s MRI, segment the different tissue types, and build a finite element model that maps the electric field throughout the brain. This allows clinicians to predict, before treatment even begins, where the fields will be strongest and weakest.²¹ For tumors in difficult locations, such as the thalamus or brainstem, where standard external electrode positions may not deliver adequate field strength, some researchers have explored modeling intracranial electrode configurations to see whether surgically placed electrodes could improve treatment of deep tumors.²² This kind of personalization is still largely a research endeavor, but Novocure has increasingly incorporated treatment planning software into its clinical workflow.

The Affordability Problem

TTFields therapy is expensive. The device itself is proprietary to Novocure, and there is no generic equivalent. A European cost-effectiveness analysis of TTFields in newly diagnosed glioblastoma found that the treatment added an average of about four months of life at an incremental cost of over €185,000 per patient. The cost per life-year gained was roughly €550,000, with sensitivity analyses showing it was essentially 0% likely to be considered cost-effective at a €100,000-per-life-year threshold.²³ In the United States, the device typically costs on the order of $21,000 per month, though insurance coverage has become more common since FDA approval.

The cost picture looks somewhat better in lung cancer when TTFields are combined with immunotherapy, as noted earlier, but the overall economic burden remains a genuine barrier to access. For a treatment that requires continuous use over many months, the cumulative cost adds up quickly. This raises the question of whether wider adoption, competition, or next-generation device designs could bring the price down, and whether better patient selection through biomarkers or computational modeling could ensure the treatment reaches those most likely to benefit rather than being applied broadly at high cost with variable returns.