Tumor Treating Fields for Mesothelioma

Tumor Treating Fields (TTFields)
Wearable device delivering 150 kHz alternating electric fields as first-line therapy for pleural mesothelioma
Device Name	Optune Lua (formerly NovoTTF-100L)
Manufacturer	NovoCure Ltd.
FDA Status	HDE approval H180002 (May 2019)
Frequency	150 kHz alternating electric fields
Pivotal Trial	STELLAR (phase 2, n=80)
Median Overall Survival	18.2 months
Used With	Pemetrexed + platinum chemotherapy

Executive Summary

Tumor Treating Fields (TTFields) is a non-invasive, device-based cancer therapy that delivers low-intensity, alternating electric fields at 150 kHz to disrupt cell division in tumor cells. Delivered through the wearable Optune Lua device (originally marketed as the NovoTTF-100L System) manufactured by NovoCure, TTFields is the only device-based therapy approved by the U.S. Food and Drug Administration for malignant pleural mesothelioma. The FDA approved the device on May 22, 2019 under a Humanitarian Device Exemption (HDE, approval number H180002) for concurrent use with pemetrexed and platinum-based chemotherapy in patients with unresectable, locally advanced or metastatic disease.

The approval was based on the STELLAR trial (NCT02397928), a phase 2, single-arm, multicenter study of 80 patients with previously untreated, unresectable pleural mesothelioma across 12 European sites. Patients treated with TTFields plus first-line chemotherapy achieved a median overall survival of 18.2 months — compared with the 12.1-month historical benchmark from the landmark Vogelzang chemotherapy trial. Because STELLAR was a single-arm study without a randomized control group, TTFields was approved under the HDE pathway — which requires a demonstration of "probable benefit" rather than the "demonstrated effectiveness" standard of full Premarket Approval (PMA).

TTFields is generally well tolerated, with the most common device-related side effect being a mild-to-moderate skin reaction underneath the transducer arrays. The therapy does not replace chemotherapy, immunotherapy, or surgery — it is added to first-line chemotherapy. Patients whose insurers deny coverage on the grounds that the HDE pathway is "investigational" may have recovery options through asbestos trust fund claims and civil litigation, where mesothelioma treatment costs can be pursued as damages.

At-a-Glance

Tumor Treating Fields for mesothelioma at a glance:

• Only FDA-approved device therapy — TTFields (Optune Lua) is the sole device-based treatment the FDA has approved for malignant pleural mesothelioma
• 150 kHz alternating electric fields — the device delivers tuned electric fields that interfere with the machinery dividing cancer cells use to separate
• 18.2-month median overall survival — the STELLAR trial's primary efficacy result in first-line pleural mesothelioma
• Approved May 2019 under HDE H180002 — a Humanitarian Device Exemption for a rare-disease population, not a full Premarket Approval
• Used with chemotherapy, not instead of it — TTFields is added to first-line pemetrexed plus cisplatin or carboplatin
• 62.2% one-year and 41.9% two-year survival — longer-term STELLAR survival milestones
• Skin reaction is the main side effect — grade 1–2 dermatitis under the arrays occurred in 66% of STELLAR patients; no treatment-related deaths were reported
• Worn on the chest as transducer arrays — patients wear adhesive electrode arrays connected to a portable field generator
• Not yet in NCCN or ASCO guidelines — major U.S. guideline bodies await phase 3 randomized data before a strong recommendation
• Historical benchmark was 12.1 months — the pre-TTFields chemotherapy-alone survival from the Vogelzang trial

Key Facts

Measure	Finding (Source)
Therapy type	Non-invasive device therapy — wearable delivery of 150 kHz alternating electric fields (Optune Lua / NovoTTF-100L)
FDA approval	Humanitarian Device Exemption H180002 — approved May 22, 2019 for unresectable pleural mesothelioma
Pivotal trial	STELLAR — phase 2, single-arm, 80 patients, 12 European sites (Ceresoli et al., Lancet Oncology, 2019)
Median overall survival	18.2 months (95% CI 12.1–25.8) — STELLAR, TTFields plus chemotherapy
Progression-free survival	7.6 months median — STELLAR
Survival milestones	62.2% at one year, 41.9% at two years — STELLAR
Main device side effect	Skin reaction (dermatitis) — grade 1–2 in 66%, grade 3 in 5%; no treatment-related deaths
Given in combination with	Pemetrexed + cisplatin or carboplatin (first-line chemotherapy)
Guideline status	Not featured in current NCCN or ASCO mesothelioma guidelines; included in German Onkopedia guidance

What Are Tumor Treating Fields (TTFields)?

Tumor Treating Fields are low-intensity, intermediate-frequency alternating electric fields delivered non-invasively to the region of the body affected by cancer. For pleural mesothelioma, the fields are tuned to 150 kHz and applied across the thorax. The therapy targets cells that are actively dividing: as a cancer cell prepares to split, it assembles a microtubule-based spindle that pulls duplicated chromosomes apart. The alternating electric fields interfere with the electrically charged proteins involved in this process, disrupting normal spindle formation and impairing the cell's ability to complete division. Because rapidly dividing cancer cells are more vulnerable to this disruption than most healthy tissue, the effect is relatively selective.

TTFields is fundamentally different from a drug. It is not swallowed, infused, or injected — it is generated by a portable medical device and delivered through adhesive transducer arrays worn on the skin. This distinction is central to how the therapy is regulated, prescribed, and covered by insurers, and it is why TTFields is classified and approved as a medical device rather than a pharmaceutical. The same underlying TTFields technology, at different frequencies, has been approved by the FDA for other cancers, including glioblastoma and non-small cell lung cancer — but each indication is authorized separately based on its own clinical evidence.

How Do Patients Use TTFields Day-to-Day?

TTFields therapy for mesothelioma is delivered through the Optune Lua system, which consists of adhesive transducer arrays placed on the front, back, and sides of the chest, connected by cable to a lightweight, portable electric field generator that a patient can carry in a bag. The therapy is designed for continuous, at-home use rather than in a clinic: patients wear the arrays throughout the day and night, removing them only for short periods for personal care such as showering and array replacement. Consistent, high daily usage is associated with better outcomes in TTFields therapy, so patients are counseled to keep the device on for as many hours per day as they can manage.

The arrays are typically changed every few days, and the skin underneath is monitored for irritation. Because the device is worn continuously alongside first-line chemotherapy, patients receive their pemetrexed and platinum infusions on the normal chemotherapy schedule while wearing the device between and during treatment cycles. The manufacturer operates a patient-support program that trains patients and caregivers on array placement, device maintenance, and skin care.

The STELLAR Trial: Design and Results

The FDA approval of TTFields for mesothelioma rests on the STELLAR trial (NCT02397928), reported by Ceresoli and colleagues in The Lancet Oncology in 2019. STELLAR was a phase 2, single-arm, multicenter study that enrolled 80 patients with previously untreated, unresectable malignant pleural mesothelioma at 12 sites across Europe between February 2015 and March 2017. All patients received TTFields at 150 kHz delivered to the thorax, combined with standard first-line chemotherapy — pemetrexed plus either cisplatin or carboplatin.

Because STELLAR had no randomized comparison group, its results were interpreted against a historical benchmark: the 12.1-month median survival reported in the pivotal Vogelzang trial that established pemetrexed-cisplatin as the standard chemotherapy for mesothelioma in 2003. Against that benchmark, the STELLAR combination produced a median overall survival of 18.2 months (95% confidence interval 12.1–25.8 months), with a median progression-free survival of 7.6 months. Survival at one year was 62.2% and at two years 41.9%. The trial met its primary endpoint of overall survival.

The single-arm design is the trial's principal limitation. Without a randomized control arm receiving chemotherapy alone, it is not possible to fully separate the contribution of TTFields from patient-selection effects and improvements in supportive care since 2003. Independent commentators have described a randomized phase 3 trial as important to confirming the true added benefit of the therapy — a caveat that continues to shape guideline and payer decisions.

Survival and Safety Data

In STELLAR, adding TTFields to first-line chemotherapy did not substantially increase serious systemic toxicity beyond what is expected from chemotherapy alone. The most common grade 3 or higher hematologic adverse events were anemia (11%), neutropenia (9%), and thrombocytopenia (5%) — consistent with the known profile of pemetrexed and platinum chemotherapy. Critically, no treatment-related deaths were reported in the trial.

The characteristic device-specific side effect of TTFields is a skin reaction beneath the transducer arrays, caused by prolonged adhesive contact and the electric fields. In STELLAR, this dermatitis was grade 1–2 (mild to moderate) in 66% of patients and grade 3 (severe) in 5%. Skin reactions are generally managed with array repositioning, topical treatments, and short treatment breaks, and rarely require permanent discontinuation. This favorable safety profile — meaningful survival signal without added systemic toxicity — is a central part of the argument for offering TTFields to appropriately selected patients.

Is TTFields FDA-Approved for Mesothelioma?

Yes — but the type of approval matters. On May 22, 2019, the FDA approved the NovoTTF-100L System (now Optune Lua) for the treatment of unresectable, locally advanced or metastatic malignant pleural mesothelioma, for use together with pemetrexed and platinum-based chemotherapy. The approval was granted under a Humanitarian Device Exemption (HDE), approval number H180002.

An HDE is a distinct regulatory pathway reserved for devices that treat rare conditions affecting a small U.S. patient population. Unlike full Premarket Approval (PMA) — which requires a device manufacturer to demonstrate effectiveness, typically through a randomized controlled trial — an HDE requires only a demonstration that the device is safe and provides "probable benefit", and that no comparable approved device is available. TTFields for mesothelioma qualified because STELLAR showed a probable-benefit survival signal and no other device was FDA-approved for this indication.

This distinction is more than a technicality. Because the mesothelioma indication rests on an HDE rather than a PMA, some insurers anchor their medical-necessity policies to the PMA standard and may treat the therapy as "investigational," even though it is genuinely FDA-approved and clinically available. Patients facing a coverage denial on those grounds can appeal using the FDA HDE approval document, the STELLAR publication, and a letter of medical necessity from their treating specialist, and may have additional recovery paths through trust fund claims and litigation.

Why Isn't TTFields in the NCCN or ASCO Guidelines?

Major U.S. oncology guideline bodies have not yet issued a strong recommendation for TTFields in mesothelioma. The therapy is not prominently featured in the current National Comprehensive Cancer Network (NCCN) or American Society of Clinical Oncology (ASCO) pleural mesothelioma guidelines. The reason is methodological rather than a judgment that the therapy does not work: both bodies generally require phase 3 randomized controlled trial evidence before a category 1 or strong-recommendation endorsement, and STELLAR was a phase 2, single-arm study. No randomized phase 3 trial of TTFields in mesothelioma has yet reported results.

Guideline coverage is not uniform internationally — the German Onkopedia guidelines, for example, do include TTFields as a treatment option for pleural mesothelioma. For patients and families, the practical takeaway is that TTFields is an FDA-approved, evidence-supported option that a mesothelioma specialist may recommend, while acknowledging that the strongest tier of guideline endorsement awaits further randomized data.

What Does TTFields Therapy Cost?

NovoCure does not publicly disclose mesothelioma-specific pricing for Optune Lua. Published estimates for TTFields therapy, drawn primarily from the device's use in glioblastoma, place the cost at roughly $21,000 per month. Because a course of therapy runs alongside chemotherapy for several months, total treatment costs can be substantial before insurance.

Coverage varies. Medicare and many private insurers cover TTFields for its longer-established indications, but for mesothelioma specifically, coverage decisions can turn on the HDE-versus-PMA distinction described above, and some payers require prior authorization or deny on investigational grounds. Patients who exhaust insurance appeals are not necessarily out of options: mesothelioma is a compensable asbestos disease, and the cost of medically necessary treatment — including device therapy — can be pursued as part of damages in asbestos trust fund claims and personal injury litigation.

Frequently Asked Questions

Is Tumor Treating Fields a drug or a device?

TTFields is a medical device, not a drug. It generates low-intensity, 150 kHz alternating electric fields that are delivered through adhesive arrays worn on the chest. Because it is a device rather than a pharmaceutical, it is regulated by the FDA's device pathway and was approved for mesothelioma under a Humanitarian Device Exemption.

Is TTFields FDA-approved for mesothelioma?

Yes. The FDA approved the device (NovoTTF-100L, now Optune Lua) for unresectable malignant pleural mesothelioma on May 22, 2019, under Humanitarian Device Exemption H180002, for use with pemetrexed and platinum chemotherapy. It is the only FDA-approved device therapy for this cancer. The HDE pathway confirms safety and probable benefit rather than the demonstrated effectiveness required for full Premarket Approval.

What did the STELLAR trial show?

STELLAR was a phase 2, single-arm trial of 80 patients with previously untreated, unresectable pleural mesothelioma. Patients treated with TTFields plus first-line chemotherapy had a median overall survival of 18.2 months, one-year survival of 62.2%, two-year survival of 41.9%, and median progression-free survival of 7.6 months — compared with the 12.1-month historical benchmark for chemotherapy alone.

What are the side effects of TTFields?

The most common device-specific side effect is a skin reaction under the transducer arrays, which was mild to moderate (grade 1–2) in 66% of STELLAR patients and severe (grade 3) in 5%. The serious systemic side effects seen in the trial — anemia, neutropenia, and thrombocytopenia — are attributable to the accompanying chemotherapy. No treatment-related deaths were reported.

Why do some insurers call TTFields investigational?

Because the mesothelioma indication was approved under a Humanitarian Device Exemption rather than full Premarket Approval, some insurers whose policies are anchored to the PMA standard treat it as investigational — even though it is FDA-approved and clinically available. Patients can appeal using the FDA HDE document, the STELLAR publication, and a physician letter of medical necessity, and may also recover treatment costs through trust fund claims or litigation.

Does TTFields replace chemotherapy or surgery?

No. TTFields is added to first-line chemotherapy (pemetrexed plus a platinum agent); it is not a substitute for chemotherapy, immunotherapy, or surgery. A mesothelioma specialist determines how it fits into an individual treatment plan.

Quick Statistics

• 150 kHz — frequency of the alternating electric fields used for pleural mesothelioma
• May 22, 2019 — date of FDA Humanitarian Device Exemption approval (H180002)
• 80 patients — enrollment in the pivotal STELLAR trial
• 12 sites — European centers participating in STELLAR
• 18.2 months — median overall survival with TTFields plus chemotherapy
• 7.6 months — median progression-free survival in STELLAR
• 62.2% / 41.9% — one-year and two-year overall survival in STELLAR
• 12.1 months — historical chemotherapy-alone survival benchmark (Vogelzang, 2003)
• 66% — STELLAR patients with grade 1–2 device-related skin reaction
• ~$21,000/month — published cost estimate for TTFields therapy

Related Pages

• Mesothelioma Treatment
• Chemotherapy for Mesothelioma
• Immunotherapy for Mesothelioma
• Radiation Therapy for Mesothelioma
• Pleural Mesothelioma
• Mesothelioma Clinical Trials

External Links

• Danziger & De Llano — Mesothelioma Treatment Overview — plain-language guide to first-line and emerging mesothelioma treatments and how treatment costs factor into compensation
• Mesothelioma Lawyers Near Me — filing guides, treatment explainers, and attorney directory
• Mesothelioma.net — patient resources on treatment options, clinical trials, and compensation