TTFields (Optune Lua / NovoTTF-100L) for Mesothelioma

Tumor Treating Fields (TTFields), delivered by the NovoTTF-100L device marketed as Optune Lua, is an FDA-approved therapy for unresectable malignant pleural mesothelioma that uses low-intensity, intermediate-frequency (150 kHz) alternating electric fields to disrupt cancer cell division. Unlike chemotherapy or immunotherapy, TTFields is a non-systemic, non-pharmacological treatment that works by interfering with the mitotic spindle during cell division, causing dividing cells to die while leaving non-dividing normal cells largely unaffected.¹

The FDA approved TTFields for mesothelioma in May 2019, making it only the second FDA-approved treatment for malignant pleural mesothelioma (after pemetrexed in 2004). This approval was based on the STELLAR trial, a single-arm phase II study that demonstrated a median overall survival of 18.2 months when TTFields was combined with standard pemetrexed and cisplatin or carboplatin chemotherapy — compared to 12.1 months with chemotherapy alone in historical controls.²

TTFields works through two primary mechanisms. First, during metaphase, the electric fields exert directional forces on charged tubulin proteins, disrupting the proper assembly of the mitotic spindle that is essential for chromosome separation. Second, during cytokinesis (the final stage of cell division), the non-uniform electric field at the cleavage furrow causes dielectrophoretic movement of charged molecules toward the furrow, leading to structural disruption and cell death. Both effects specifically target dividing cells, giving TTFields a favorable side effect profile.³

The treatment is delivered through adhesive transducer arrays placed on the patient's torso, connected to a portable battery-powered device that can be carried in a shoulder bag. Patients wear the device for a recommended minimum of 18 hours per day, and clinical data shows that greater daily usage correlates with better outcomes. The main side effect is skin irritation under the transducer arrays, which can be managed with topical treatments and array repositioning.²

TTFields is used concurrently with first-line chemotherapy for unresectable malignant pleural mesothelioma:²

Standard TTFields Protocol

• Device setup — Novocure provides in-home training by a device support specialist who maps transducer array placement on the patient's torso based on tumor location
• Transducer arrays — Four arrays (two pairs) are placed on the front, back, and sides of the torso over the region of the tumor
• Usage target — Minimum 18 hours per day; arrays are replaced every 3–4 days, requiring skin shaving and cleaning at the application sites
• Concurrent chemotherapy — Pemetrexed 500 mg/m² + cisplatin 75 mg/m² (or carboplatin AUC 5) every 21 days for up to 6 cycles
• Maintenance — TTFields is continued after chemotherapy completion until disease progression, for a second-line treatment, or until no longer tolerated

STELLAR Trial Results

The pivotal STELLAR trial enrolled 80 patients with unresectable, previously untreated malignant pleural mesothelioma:²

• Median overall survival — 18.2 months (vs. 12.1 months historical control with chemotherapy alone)
• 1-year survival rate — 62%
• 2-year survival rate — 32%
• Median progression-free survival — 7.6 months
• Overall response rate — 40%

Dose-Response Relationship

Analysis of the STELLAR data revealed a clear correlation between daily TTFields usage and survival outcomes. Patients who wore the device for ≥18 hours daily had significantly better outcomes than those with lower compliance. This underscores the importance of maximizing device wear time, despite the practical challenges of wearing the device around the clock.²

TTFields combined with chemotherapy has demonstrated substantial survival improvements compared to historical chemotherapy-alone data:²

• Median overall survival — 18.2 months with TTFields + chemo vs. 12.1 months with chemo alone (historical control), representing a 50% improvement
• Long-term survivors — 32% of patients alive at 2 years, compared to approximately 20% with chemotherapy alone historically
• Quality of life — No significant deterioration in quality of life scores during TTFields treatment, which is notable given the device is worn nearly continuously
• Compliance impact — Patients wearing the device ≥18 hours/day had better outcomes, emphasizing the importance of adherence
• Epithelioid subtype — Patients with epithelioid histology tended to derive the greatest benefit from TTFields

Living with TTFields therapy requires adapting daily routines to the wearable device, but side effects are minimal compared to systemic treatments:²

• Skin irritation — The most common side effect, affecting 40–50% of patients. Manifests as redness, itching, or mild rash under the transducer arrays. Managed by rotating array placement, using topical corticosteroid creams, keeping the skin clean and dry, and allowing brief recovery periods
• Device comfort — The device and battery pack weigh approximately 2.7 pounds and are carried in a shoulder bag or backpack. Most patients adapt within the first week. Sleeping with the device is manageable with practice
• Daily routine — Arrays are removed briefly for showering (typically 30–60 minutes), and the skin must be shaved and cleaned before applying fresh arrays every 3–4 days. Plan for about 30 minutes of array maintenance time at each change
• Physical activity — Normal activities, including light exercise, are possible while wearing the device. The device should not be exposed to water, which limits swimming
• No systemic side effects — Unlike chemotherapy, TTFields does not cause nausea, hair loss, myelosuppression, or organ toxicity. Side effects from concurrent chemotherapy are separate and managed independently
• Support resources — Novocure provides 24/7 device support and assigns a device support specialist to each patient for training, troubleshooting, and ongoing assistance