What Are Checkpoint Inhibitors?
Checkpoint inhibitors are a type of immunotherapy that helps your immune system recognize and attack cancer cells. Cancer cells often use “checkpoints” to hide from the immune system. These drugs block those checkpoints, releasing the brakes on your immune response.
Think of it this way: T cells, the immune system’s attack cells, have proteins on their surface that act like an “off switch.” Cancer cells can flip that switch, telling T cells to stand down. Checkpoint inhibitors block this interaction, keeping T cells active and able to fight cancer.
The FDA approval of nivolumab plus ipilimumab in October 2020 was the first new systemic therapy approved for mesothelioma in 15 years, since pemetrexed in 2004.
FDA-Approved Checkpoint Inhibitors for Mesothelioma
As of 2026, the FDA has approved one checkpoint inhibitor combination specifically for mesothelioma:
Nivolumab (Opdivo) + Ipilimumab (Yervoy)
Approval: October 2, 2020
Indication: First-line treatment of adults with unresectable malignant pleural mesothelioma
| Drug | Target | How It Works |
|---|---|---|
| Nivolumab (Opdivo) | PD-1 | Blocks the PD-1 receptor on T cells |
| Ipilimumab (Yervoy) | CTLA-4 | Blocks CTLA-4, boosting T cell activation |
Dosing schedule:
- Nivolumab: 360 mg every 3 weeks
- Ipilimumab: 1 mg/kg every 6 weeks
- Treatment continues until disease progression or unacceptable toxicity
How Checkpoint Inhibitors Work
PD-1/PD-L1 Pathway
The PD-1 (programmed death-1) protein sits on T cells. When cancer cells express PD-L1, they bind to PD-1 and send a “stop” signal to T cells.
PD-1 inhibitors (nivolumab, pembrolizumab):
- Block the PD-1 receptor on T cells
- Prevent cancer cells from sending the “stop” signal
- Allow T cells to remain active and attack cancer
CTLA-4 Pathway
CTLA-4 is another checkpoint that normally prevents T cells from becoming fully activated. It competes with a protein called CD28, which T cells need for activation.
CTLA-4 inhibitors (ipilimumab):
- Block CTLA-4 on T cells
- Allow CD28 to fully activate T cells
- Boost the overall immune response against cancer
Combining PD-1 and CTLA-4 inhibitors produces better results than either alone. They target different stages of the immune response, creating a more comprehensive attack on cancer.
Clinical Trial Evidence
CheckMate 743 Trial
The landmark CheckMate 743 trial led to FDA approval. This Phase 3 trial enrolled 605 patients with previously untreated unresectable malignant pleural mesothelioma.
| Outcome | Nivo + Ipi | Chemotherapy |
|---|---|---|
| Median overall survival | 18.1 months | 14.1 months |
| 1-year survival | 68% | 58% |
| 2-year survival | 41% | 27% |
| 3-year survival | 23% | 15% |
Key findings:
- 22% reduction in risk of death compared to chemotherapy
- Benefit seen across all cell types
- Sarcomatoid and biphasic types showed greatest benefit
- Response can be durable (lasting years in some patients)
Cell Type Responses
Not all mesothelioma cell types respond equally:
| Cell Type | Checkpoint Inhibitor Benefit | Notes |
|---|---|---|
| Sarcomatoid | Highest | 18.3 vs 8.8 months (dramatic improvement) |
| Biphasic | High | 18.1 vs 13.6 months |
| Epithelioid | Moderate | 18.7 vs 16.2 months |
If you have sarcomatoid or biphasic mesothelioma, checkpoint inhibitors offer a significant advantage over chemotherapy. Ask your oncologist specifically about immunotherapy.
Other Checkpoint Inhibitors Under Study
Pembrolizumab (Keytruda)
Pembrolizumab is a PD-1 inhibitor being studied in mesothelioma:
KEYNOTE trials:
- Combined with chemotherapy
- Some positive results in combination settings
- Not yet FDA-approved specifically for mesothelioma
Durvalumab (Imfinzi)
Durvalumab is a PD-L1 inhibitor (targets the ligand rather than the receptor):
DREAM3R trial results:
- Durvalumab + chemotherapy: 20.4 months median survival
- One of the longest survival figures reported in mesothelioma trials
Atezolizumab (Tecentriq)
Another PD-L1 inhibitor being tested:
- Alliance A092001 trial ongoing
- Combined with bevacizumab (Avastin) and chemotherapy
- Targets both immune checkpoints and tumor blood supply
Tremelimumab
A CTLA-4 inhibitor similar to ipilimumab:
- Being studied in combination regimens
- SMARTEST trial combining with durvalumab and other treatments
Who Should Receive Checkpoint Inhibitors?
Good Candidates
Checkpoint inhibitors may be recommended if you have:
- Unresectable pleural mesothelioma: Surgery not an option
- Previously untreated disease: As first-line therapy
- Adequate performance status: Well enough to tolerate treatment
- Sarcomatoid or biphasic cell type: Greatest benefit over chemotherapy
Factors That May Predict Response
| Factor | Better Response | Worse Response |
|---|---|---|
| Cell type | Sarcomatoid | Epithelioid (still benefits) |
| PD-L1 expression | Higher | Very low |
| Tumor burden | Lower | Very high |
| Performance status | Good (ECOG 0-1) | Poor |
When Checkpoint Inhibitors May Not Be Appropriate
- Autoimmune diseases (lupus, rheumatoid arthritis)
- Prior organ transplant
- Active infections
- Pregnancy
- Severely compromised immune system
If you have an autoimmune condition, discuss risks carefully with your oncologist. Checkpoint inhibitors can worsen autoimmune diseases, though some patients can still be treated with close monitoring.
Side Effects of Checkpoint Inhibitors
Checkpoint inhibitors cause different side effects than chemotherapy because they stimulate the immune system. The immune system can sometimes attack healthy tissue, causing immune-related adverse events (irAEs).
Common Side Effects (occur in more than 10% of patients)
| Side Effect | Frequency | Management |
|---|---|---|
| Fatigue | 30-40% | Rest, activity pacing |
| Skin rash | 20-30% | Topical steroids, antihistamines |
| Diarrhea | 15-25% | Dietary changes, anti-diarrheal medications |
| Nausea | 15-20% | Anti-nausea medications |
| Pruritus (itching) | 10-15% | Antihistamines, topical treatments |
Immune-Related Adverse Events
More serious but less common side effects requiring immediate attention:
Pneumonitis (lung inflammation):
- Symptoms: New or worsening shortness of breath, cough
- Frequency: 5-10%
- Treatment: Steroids, may require stopping therapy
Colitis (intestinal inflammation):
- Symptoms: Severe diarrhea, abdominal pain, blood in stool
- Frequency: 5-8%
- Treatment: Steroids, may require hospitalization
Hepatitis (liver inflammation):
- Symptoms: Often no symptoms, detected by blood tests
- Frequency: 5-10%
- Treatment: Steroids, dose adjustment
Endocrine disorders:
- Thyroid dysfunction: 10-15%
- Hypophysitis (pituitary inflammation): 1-5%
- Adrenal insufficiency: 1-2%
- Treatment: Hormone replacement if needed
Report any new or worsening symptoms immediately. Early treatment of immune-related side effects leads to better outcomes. Some side effects require steroids or treatment interruption.
Checkpoint Inhibitors vs. Chemotherapy
| Factor | Checkpoint Inhibitors | Chemotherapy |
|---|---|---|
| Median survival | 18+ months | 12-14 months |
| How it works | Activates immune system | Kills dividing cells |
| Main side effects | Immune-related | Blood counts, nausea |
| Hair loss | Rare | Common with some regimens |
| Long-term survivors | More common | Less common |
| Works for everyone | No (need immune response) | Generally yes |
Combining Checkpoint Inhibitors with Other Treatments
With Chemotherapy
Adding checkpoint inhibitors to chemotherapy may improve outcomes:
- DREAM3R trial: durvalumab + chemo = 20.4 months survival
- KEYNOTE trials testing pembrolizumab + chemo
- May become standard approach
With Surgery
Neoadjuvant (before surgery) checkpoint inhibitors:
- Hopkins neoadjuvant trial showing promise
- May shrink tumors before surgery
- Post-surgery maintenance also being studied
With Radiation
Combining radiation with immunotherapy:
- IMPRINT trial testing pembrolizumab + pleural radiation
- Radiation may “prime” immune response
- Called abscopal effect
Current Clinical Trials (2026)
First-Line Trials
DREAM3R: Durvalumab + chemotherapy vs chemotherapy vs nivo/ipi
- Results: 20.4 months survival with durvalumab combination
Alliance A092001: Atezolizumab + bevacizumab + chemotherapy
- Ongoing enrollment
- Multiple US sites
Combination Trials
SMARTEST: Tremelimumab + durvalumab + radiation + surgery
- Multimodal approach
- International sites
Hopkins neoadjuvant trial: Immunotherapy before surgery
- For surgical candidates
- Evaluating pathologic response
How to Access Checkpoint Inhibitors
FDA-Approved Treatment
If you have unresectable pleural mesothelioma:
- Discuss nivolumab + ipilimumab with your oncologist
- Insurance typically covers FDA-approved treatments
- Can be administered at most cancer centers
Clinical Trials
For newer combinations or different settings:
- Search ClinicalTrials.gov for “mesothelioma checkpoint inhibitor”
- Ask your oncologist about trial eligibility
- Contact major mesothelioma centers
Are checkpoint inhibitors better than chemotherapy for mesothelioma?▼
For most patients, checkpoint inhibitors provide longer survival (18 vs 14 months) with different side effects. The benefit is most dramatic for sarcomatoid and biphasic cell types. Some patients have durable responses lasting years.
What is the difference between PD-1 and CTLA-4 inhibitors?▼
PD-1 inhibitors (nivolumab) block the “off switch” on T cells. CTLA-4 inhibitors (ipilimumab) boost T cell activation. Using both together creates a more comprehensive immune response.
Will checkpoint inhibitors work for my mesothelioma?▼
Response varies by individual. Factors that predict better response include non-epithelioid cell type, higher PD-L1 expression, and good overall health. Your oncologist can help assess your specific situation.
What side effects should I watch for?▼
Common side effects include fatigue, rash, and diarrhea. More serious immune-related effects (pneumonitis, colitis, hepatitis, thyroid problems) require prompt attention. Report any new symptoms to your care team immediately.
Can I receive checkpoint inhibitors if I have an autoimmune disease?▼
It depends on the specific condition and severity. Some patients with autoimmune conditions can receive checkpoint inhibitors with close monitoring. Discuss the risks and benefits with your oncologist.
References
The Lancet. (2021). First-line nivolumab plus ipilimumab in unresectable malignant pleural mesothelioma (CheckMate 743): a multicentre, randomised, open-label, phase 3 trial.
https://pubmed.ncbi.nlm.nih.gov/33485464/
Annals of Oncology. (2022). Three-year outcomes from CheckMate 743: First-line nivolumab plus ipilimumab versus chemotherapy in patients with unresectable malignant pleural mesothelioma.
https://pubmed.ncbi.nlm.nih.gov/35124183/
FDA. (2020). FDA approves nivolumab plus ipilimumab for unresectable malignant pleural mesothelioma.
https://www.fda.gov/drugs/resources-information-approved-drugs/fda-approves-nivolumab-and-ipilimumab-unresectable-malignant-pleural-mesothelioma
Journal of Thoracic Oncology. (2022). Immune checkpoint inhibitors in malignant pleural mesothelioma: a systematic review and meta-analysis.
https://pubmed.ncbi.nlm.nih.gov/35065282/
ESMO Congress. (2025). DREAM3R: Durvalumab plus chemotherapy versus chemotherapy in malignant pleural mesothelioma.
https://oncologypro.esmo.org/meeting-resources/esmo-congress