Mesothelioma Immunotherapy

How Immunotherapy Works

Immunotherapy is a type of cancer treatment that harnesses the power of the body's own immune system to fight cancer. Unlike chemotherapy, which directly kills dividing cells, immunotherapy works by removing the "brakes" that cancer cells use to hide from the immune system, allowing the body's natural defenses to recognize and attack mesothelioma cells.

The Immune Checkpoint System

The immune system uses a series of molecular "checkpoints" — proteins on immune cells that act as on/off switches — to prevent immune cells from attacking the body's own healthy tissues. Cancer cells can hijack these checkpoints to avoid immune detection. In mesothelioma, tumor cells exploit two key checkpoint pathways:

• PD-1/PD-L1 pathway — mesothelioma cells express a protein called PD-L1 on their surface. When PD-L1 binds to the PD-1 receptor on T-cells (a type of immune cell), it sends a "don't attack" signal, effectively hiding the cancer from the immune system. Nivolumab (Opdivo) and pembrolizumab (Keytruda) block the PD-1 receptor, preventing this signal and allowing T-cells to recognize and kill cancer cells.
• CTLA-4 pathway — CTLA-4 is another checkpoint protein that regulates T-cell activation at an earlier stage. When CTLA-4 is activated, it suppresses the T-cell response. Ipilimumab (Yervoy) blocks CTLA-4, amplifying the immune system's activation against cancer cells. By blocking both PD-1 and CTLA-4 simultaneously, the combination of nivolumab and ipilimumab creates a more powerful anti-tumor immune response.

Why Immunotherapy Works for Mesothelioma

Mesothelioma has several characteristics that make it particularly responsive to immunotherapy:

• Chronic inflammation — asbestos fibers cause chronic inflammation in the pleural or peritoneal lining, which creates an immune-rich tumor microenvironment that can be activated by checkpoint inhibitors
• High PD-L1 expression — many mesothelioma tumors express high levels of PD-L1, particularly sarcomatoid and biphasic subtypes, indicating active immune evasion that can be reversed with PD-1 blockade
• T-cell infiltration — mesothelioma tumors are often infiltrated by T-cells, indicating that the immune system is attempting to fight the cancer but is being suppressed by checkpoint mechanisms

Pembrolizumab (Keytruda) & Other Checkpoint Inhibitor Trials

While nivolumab + ipilimumab is the only FDA-approved immunotherapy combination for mesothelioma, several other checkpoint inhibitors have shown activity in clinical trials. Pembrolizumab (Keytruda), a PD-1 inhibitor manufactured by Merck, has been the most extensively studied of these alternative immunotherapy agents.

KEYNOTE-028 Trial

• Study design — Phase Ib trial of pembrolizumab in patients with PD-L1-positive advanced pleural mesothelioma who had progressed on prior chemotherapy
• Key results — objective response rate of 20%, disease control rate of 72%, median progression-free survival of 5.4 months, and median overall survival of 18 months in responding patients
• Significance — demonstrated that single-agent PD-1 inhibition has meaningful activity in previously treated mesothelioma, particularly in PD-L1-positive tumors

PROMISE-meso Trial

• Study design — randomized Phase III trial comparing pembrolizumab to standard single-agent chemotherapy (gemcitabine or vinorelbine) in previously treated mesothelioma patients
• Key results — pembrolizumab demonstrated a higher overall response rate and longer duration of response compared to chemotherapy, though no significant difference in overall survival was observed in the overall study population
• Significance — suggested that while pembrolizumab produces meaningful responses in a subset of patients, patient selection (particularly by PD-L1 status and cell type) is important for optimizing outcomes

Other Immunotherapy Agents Under Investigation

• Durvalumab (Imfinzi) — an anti-PD-L1 antibody being studied in combination with chemotherapy and with other immunotherapy agents for mesothelioma
• Atezolizumab (Tecentriq) — another anti-PD-L1 antibody with ongoing clinical trials in mesothelioma, including combination approaches with bevacizumab
• Tremelimumab — an anti-CTLA-4 antibody that has been studied in combination with durvalumab for mesothelioma and other solid tumors

TTFields, Clinical Trials & Emerging Treatments

Beyond checkpoint inhibitor immunotherapy, several emerging treatment approaches are being studied for mesothelioma. These therapies represent the next frontier of mesothelioma treatment and may offer additional options for patients who have exhausted standard treatments or who wish to explore cutting-edge approaches through clinical trials.

Tumor Treating Fields (TTFields / NovoTTF-100L / Optune Lua)

Tumor Treating Fields (TTFields) is a non-invasive treatment that uses low-intensity, alternating electric fields to disrupt cancer cell division. The device, marketed as Optune Lua (NovoTTF-100L), consists of adhesive transducer arrays placed on the patient's torso that deliver continuous electric fields targeting the chest area.

• STELLAR Trial — the Phase II STELLAR trial studied TTFields combined with pemetrexed + cisplatin or carboplatin as first-line treatment for unresectable malignant pleural mesothelioma. The trial reported a median overall survival of 18.2 months with the combination, compared to the historical benchmark of 12.1 months for chemotherapy alone.
• FDA approval — TTFields in combination with pemetrexed and platinum-based chemotherapy received FDA approval for the treatment of unresectable, locally advanced or metastatic malignant pleural mesothelioma
• How it works — TTFields disrupt cell division by interfering with the mitotic spindle formation and causing abnormal cell death in dividing cancer cells. The electric fields selectively affect rapidly dividing cells (cancer) while causing minimal damage to normal, slowly dividing tissue.
• Treatment protocol — patients wear the transducer arrays for at least 18 hours per day throughout treatment. The device is portable and battery-powered, allowing patients to maintain their daily activities during treatment.

Other Emerging Therapies in Clinical Trials

• CAR-T cell therapy — chimeric antigen receptor T-cell therapy engineers a patient's own immune cells to target mesothelin, a protein highly expressed on mesothelioma cells. Early clinical trials have shown promising results, with some patients achieving complete or partial responses.
• Gene therapy — approaches using modified viruses to deliver tumor-suppressing genes directly into mesothelioma cells are in clinical testing. The goal is to restore tumor suppressor function (such as p16 or BAP1) that is lost in mesothelioma.
• Anti-angiogenic agents — drugs that inhibit blood vessel growth to tumors, such as bevacizumab (Avastin), have shown activity when combined with chemotherapy in the MAPS trial (18.8 months median survival vs. 16.1 months with chemotherapy alone).
• Oncolytic virus therapy — engineered viruses that selectively infect and destroy cancer cells while stimulating an anti-tumor immune response are being tested in mesothelioma clinical trials.
• Combination immunotherapy + chemotherapy — multiple trials are studying whether adding chemotherapy to checkpoint inhibitors provides better outcomes than either approach alone.