Immunotherapy for Mesothelioma

Immunotherapy for mesothelioma uses drugs that harness the body's immune system to recognize and attack cancer cells. The FDA-approved immunotherapy regimen for mesothelioma is nivolumab (Opdivo) combined with ipilimumab (Yervoy), which targets two distinct immune checkpoint pathways — PD-1 and CTLA-4 — to release the brakes on the anti-tumor immune response.¹

On October 2, 2020, the FDA approved nivolumab plus ipilimumab as the first-line treatment for unresectable malignant pleural mesothelioma. This approval was based on the CheckMate 743 trial, which demonstrated a significant overall survival benefit compared to standard pemetrexed/platinum chemotherapy. This was the first new systemic therapy approved for mesothelioma in 16 years, since pemetrexed's approval in 2004.²

The survival benefit of immunotherapy was most pronounced in patients with sarcomatoid and biphasic histology — subtypes that historically respond poorly to chemotherapy. For epithelioid mesothelioma, the survival difference between immunotherapy and chemotherapy was smaller, making the choice of first-line therapy a shared decision between the patient and oncologist.²

Immunotherapy represents a paradigm shift in mesothelioma treatment. Unlike chemotherapy, which directly kills dividing cells, immunotherapy works by restoring the immune system's ability to detect and eliminate cancer cells. This can produce durable responses lasting years in a subset of patients, even after treatment is discontinued.¹

FDA-approved regimen: Nivolumab + Ipilimumab

The approved first-line immunotherapy regimen for unresectable malignant pleural mesothelioma is:²

• Nivolumab — 360 mg IV every 3 weeks (or 3 mg/kg every 2 weeks)
• Ipilimumab — 1 mg/kg IV every 6 weeks
• Duration — Treatment continues for up to 2 years or until disease progression or unacceptable toxicity²

How immune checkpoint inhibitors work

Cancer cells evade the immune system by exploiting inhibitory pathways (checkpoints) that normally prevent autoimmune responses:

• PD-1/PD-L1 pathway — Mesothelioma cells express PD-L1 (programmed death-ligand 1) on their surface, which binds to PD-1 receptors on T cells, sending an "off" signal that prevents the T cells from attacking. Nivolumab blocks PD-1 on T cells, removing this inhibitory signal and allowing T cells to recognize and kill cancer cells.³
• CTLA-4 pathway — CTLA-4 is a checkpoint receptor on T cells that downregulates T cell activation in lymph nodes. Ipilimumab blocks CTLA-4, enhancing T cell priming and activation. The combination of PD-1 and CTLA-4 blockade has a synergistic effect, producing more robust anti-tumor immune responses than either agent alone.³

CheckMate 743 trial results

The CheckMate 743 trial enrolled 605 patients with previously untreated, unresectable malignant pleural mesothelioma and randomized them to nivolumab/ipilimumab or pemetrexed/platinum chemotherapy:²

• Median overall survival: 18.1 months (immunotherapy) vs. 14.1 months (chemotherapy)
• 2-year overall survival rate: 41% vs. 27%
• Non-epithelioid subgroup: Median OS 18.1 months vs. 8.8 months — a dramatic benefit
• Epithelioid subgroup: Median OS 18.7 months vs. 16.5 months — a more modest benefit
• Objective response rate: 40% (immunotherapy) vs. 43% (chemotherapy)²

Notably, while objective response rates were similar, immunotherapy responses tended to be more durable, with some patients maintaining tumor control for years.²

Other immunotherapy approaches

• Single-agent nivolumab or pembrolizumab — Used in the second-line setting (after chemotherapy failure). The CONFIRM trial showed single-agent nivolumab improved overall survival compared to placebo in previously treated mesothelioma patients.⁴
• Chemotherapy + immunotherapy combinations — Trials investigating pemetrexed/platinum combined with immune checkpoint inhibitors (e.g., the IND.227/DREAM trial with durvalumab, the BEAT-meso trial with atezolizumab plus bevacizumab) aim to combine the benefits of both approaches.⁵
• Tumor treating fields (TTFields) + immunotherapy — The STELLAR trial evaluated TTFields in combination with chemotherapy, and ongoing research explores TTFields combined with immunotherapy.⁵
• Adoptive cell therapy and CAR-T cells — Early-phase clinical trials are investigating engineered T cells targeting mesothelin, a protein highly expressed on mesothelioma cells.⁵

The CheckMate 743 trial established new survival benchmarks for first-line immunotherapy in mesothelioma:²

• Overall population — Median OS 18.1 months; 2-year OS rate 41%; 3-year OS rate 23%
• Non-epithelioid histology — Median OS 18.1 months (vs. 8.8 months with chemo) — a doubling of survival
• Epithelioid histology — Median OS 18.7 months (vs. 16.5 months with chemo) — a more modest benefit²

A key advantage of immunotherapy is the potential for durable responses. Unlike chemotherapy, where responses are typically time-limited and followed by disease progression, some immunotherapy responders maintain disease control for extended periods (3+ years), even after completing the maximum 2-year treatment course. This "tail" on the survival curve represents a meaningful proportion of patients who derive long-term benefit.²

Predictive biomarkers

Research is ongoing to identify biomarkers that predict which patients are most likely to benefit from immunotherapy:³

• PD-L1 expression — Higher PD-L1 expression on tumor cells is associated with greater immunotherapy benefit in some studies, though PD-L1-negative patients can also respond.
• Tumor mutational burden (TMB) — Mesothelioma has a relatively low TMB compared to other cancers, which may limit the proportion of patients who respond. However, the sarcomatoid subtype tends to have higher TMB, which may explain its greater immunotherapy sensitivity.
• Histological subtype — Non-epithelioid histology is the strongest predictor of immunotherapy benefit in CheckMate 743. For epithelioid mesothelioma, the decision between immunotherapy and chemotherapy is more nuanced.²

Managing immunotherapy requires understanding its unique side effect profile, which differs fundamentally from chemotherapy side effects.

Immune-related adverse events (irAEs)

Because immunotherapy activates the immune system broadly, it can cause inflammation in healthy organs — termed immune-related adverse events. These can affect virtually any organ system:⁶

• Skin — Rash, pruritus (itching), vitiligo. The most common irAE (30–40% of patients).
• Gastrointestinal — Diarrhea, colitis (colon inflammation). More common with ipilimumab.
• Endocrine — Thyroiditis (thyroid inflammation), hypothyroidism, hypophysitis (pituitary inflammation), adrenal insufficiency. Endocrine irAEs may require lifelong hormone replacement.
• Hepatic — Hepatitis (liver inflammation) with elevated liver enzymes.
• Pulmonary — Pneumonitis (lung inflammation). Particularly important in mesothelioma patients who may already have compromised lung function.
• Rare but serious — Myocarditis (heart inflammation), nephritis (kidney inflammation), neurological effects (encephalitis, myasthenia gravis-like syndromes).⁶

Key management principles:

• Report any new symptoms promptly — early detection and treatment of irAEs prevents them from becoming severe or life-threatening
• Most irAEs are treated with corticosteroids (prednisone or methylprednisolone) and temporary immunotherapy interruption
• Severe irAEs (grade 3–4) typically require permanent discontinuation of ipilimumab, though nivolumab may be resumed after recovery
• Carry an immunotherapy patient card that lists your medications and treating oncologist's contact information
• Inform all healthcare providers (including emergency departments, dentists, and other specialists) that you are receiving immunotherapy, as irAEs can mimic other conditions
• Regular blood work (thyroid function, liver function, blood counts) monitors for subclinical irAEs⁶

Despite the complexity of irAE management, many patients tolerate immunotherapy well and report better overall quality of life compared to chemotherapy, with less nausea, fatigue, and myelosuppression.²