ATOMIC-Meso: Quadrupled 3-Year Survival
The ATOMIC-Meso trial showed pegargiminase plus chemotherapy quadrupled 3-year survival rates in nonepithelioid mesothelioma, the most aggressive subtype.
Key Trial Results
| Outcome | Pegargiminase + Chemo | Placebo + Chemo |
|---|---|---|
| Median overall survival | 9.3 months | 7.7 months |
| Median PFS | 6.2 months | 5.6 months |
| 3-year survival | 4x higher | Baseline |
| Improvement | +1.6 months (+21%) | : |
The ATOMIC-Meso trial demonstrated that adding pegargiminase to standard chemotherapy significantly extends survival in nonepithelioid mesothelioma, the most aggressive and treatment-resistant form of the disease. The results were published in JAMA Oncology.
Why This Matters
The Problem: Nonepithelioid Mesothelioma
Mesothelioma has three main cell types:
| Type | % of Cases | Prognosis | Treatment Response |
|---|---|---|---|
| Epithelioid | ~60% | Best | Responds to standard treatment |
| Sarcomatoid | ~15% | Worst | Poor response to chemo |
| Biphasic | ~25% | Variable | Mixed response |
Patients with sarcomatoid or biphasic (collectively “nonepithelioid”) mesothelioma have historically had few effective options. These aggressive subtypes respond poorly to standard chemotherapy and even immunotherapy.
ATOMIC-Meso Targeted This Gap
The trial specifically enrolled patients with nonepithelioid mesothelioma, a population often excluded from or underrepresented in clinical trials.
How Pegargiminase Works
The Science of Arginine Depletion
Pegargiminase (ADI-PEG20) works through a completely different mechanism than chemotherapy or immunotherapy:
- Normal cells can make their own arginine (an amino acid)
- Some cancer cells lose the enzyme (ASS1) needed to make arginine
- These cancer cells depend on external arginine to survive
- Pegargiminase destroys arginine in the bloodstream
- ASS1-deficient cancer cells starve and die
This “arginine depletion” strategy exploits a metabolic weakness specific to certain cancers.
Why It Works in Nonepithelioid Mesothelioma
Studies show that nonepithelioid mesothelioma cells frequently have low or absent ASS1 expression, making them particularly vulnerable to arginine depletion.
Trial Design
How ATOMIC-Meso Was Set Up
| Characteristic | Detail |
|---|---|
| Trial name | ATOMIC-Meso |
| Phase | 2-3, randomized, double-blind |
| Centers | 43 sites in 5 countries |
| Enrollment period | August 2017 - August 2021 |
| Patients | 249 |
| Population | Nonepithelioid pleural mesothelioma |
| Treatment line | First-line (treatment-naive) |
What Patients Received
| Arm | Treatment |
|---|---|
| Experimental | Pegargiminase + pemetrexed + platinum |
| Control | Placebo + pemetrexed + platinum |
All patients received standard chemotherapy; the question was whether adding pegargiminase would improve outcomes.
Detailed Results
Survival and Progression Results
| Metric | Pegargiminase | Placebo | Improvement |
|---|---|---|---|
| Median OS | 9.3 months | 7.7 months | +1.6 months |
| Hazard ratio (death) | 0.71 | : | 29% risk reduction |
| Median PFS | 6.2 months | 5.6 months | +0.6 months |
| Hazard ratio (progression) | 0.65 | : | 35% risk reduction |
Long-Term Survival
The most striking finding was the impact on long-term survival:
| Timepoint | Pegargiminase | Placebo | Difference |
|---|---|---|---|
| 3-year survival | ~16% | ~4% | 4x higher |
Pegargiminase quadrupled the proportion of patients alive at 3 years.
Safety Profile
| Adverse Event | Pegargiminase | Placebo |
|---|---|---|
| Grade 3-4 events | 28.8% | 16.9% |
| Drug hypersensitivity | 2.4% | : |
| Skin reactions | 1.6% | : |
The higher rate of Grade 3-4 events with pegargiminase reflects its mechanism of action, but serious adverse events remained manageable.
Comparison to Other Treatments
In Nonepithelioid Mesothelioma Specifically
| Treatment | Median OS | Notes |
|---|---|---|
| Chemotherapy alone | 7.7 months | ATOMIC-Meso control arm |
| Pegargiminase + chemo | 9.3 months | ATOMIC-Meso experimental |
| Opdivo + Yervoy | 18.1 months | All cell types; nonepithelioid benefit unclear |
For the specific nonepithelioid population, pegargiminase represents a meaningful improvement over standard chemotherapy.
Current Availability
Regulatory Status
Pegargiminase has not yet received FDA approval for mesothelioma. The ATOMIC-Meso results may support future approval applications.
Ongoing Research
The drug is being studied in several other cancers with ASS1 deficiency:
- Sarcoma
- Glioblastoma
- Hepatocellular carcinoma
The mesothelioma success validates arginine depletion as a viable cancer treatment strategy.
What This Means for Patients
For Patients with Nonepithelioid Mesothelioma
If you have sarcomatoid or biphasic mesothelioma, ask your oncologist about arginine depletion trials, which may still be enrolling at academic centers. Consider biomarker testing for ASS1 status, because low expression appears to predict response to pegargiminase. And keep in mind that new treatments are emerging specifically for the aggressive subtypes that historically had the fewest options.
For All people with mesothelioma
ATOMIC-Meso demonstrates that even the most challenging mesothelioma subtypes can be treated effectively with the right approach. The key is matching treatments to tumor biology.
The Bigger Picture
The ATOMIC-Meso trial represents a shift toward precision oncology in mesothelioma:
- Traditional approach: Same treatment for all patients
- Precision approach: Match treatment to tumor characteristics
As we learn more about mesothelioma biology, more targeted treatments like pegargiminase may emerge.
If you have sarcomatoid or biphasic mesothelioma, ask your oncologist about arginine depletion therapy and ASS1 biomarker testing. These aggressive subtypes have historically had few effective options, but ATOMIC-Meso shows that targeted approaches can work.
Reader Q&A
Frequently Asked Questions
What is nonepithelioid mesothelioma?
Mesothelioma has three cell types: epithelioid (60% of cases, best prognosis), sarcomatoid (15% of cases, worst prognosis), and biphasic (25% of cases, mixed). Sarcomatoid and biphasic are collectively called “nonepithelioid” and are more aggressive and treatment-resistant than epithelioid mesothelioma.
How does pegargiminase work?
Pegargiminase (ADI-PEG20) works by destroying arginine, an amino acid, in the bloodstream. Normal cells can make their own arginine, but some cancer cells (particularly nonepithelioid mesothelioma) have lost the enzyme (ASS1) needed to produce it. Without external arginine, these cancer cells starve and die.
Is pegargiminase FDA approved?
Not yet. Pegargiminase has not received FDA approval for mesothelioma. The ATOMIC-Meso results may support future approval applications. The drug is also being studied in sarcoma, glioblastoma, and liver cancer.
How significant is quadrupling 3-year survival?
For people with nonepithelioid mesothelioma, this is substantial. These aggressive subtypes have historically had very poor outcomes with standard chemotherapy. Moving from 4% to 16% three-year survival, while still modest, represents meaningful progress for a patient population with few effective options.
How do you treat biphasic mesothelioma?
People with biphasic mesothelioma receive treatments including immunotherapy with nivolumab plus ipilimumab as a first-line option for pleural cases, chemotherapy such as pemetrexed with cisplatin, surgery like pleurectomy with decortication or cytoreduction with HIPEC for peritoneal disease, and radiation. Multimodal approaches combining these therapies show responses in case reports, with one biphasic pleural case achieving no recurrence 11 months after chemotherapy and surgery. Immunotherapy extends survival beyond 20 months in some previously treated pleural patients, while chemotherapy alone yields about 12-month median survival and 17% 3-year rates per NCDB data. Emerging options like pegargiminase with chemotherapy target sarcomatoid components in biphasic tumors. Treatment selection depends on cell ratio, stage, location, and health.
What is a biphasic mesothelioma pattern?
Biphasic mesothelioma contains both epithelioid and sarcomatoid cells, with a diagnosis requiring at least 10% of each cell type in tumor tissue examined via biopsy. Epithelioid cells are cube-shaped or elongated and form structured patterns, while sarcomatoid cells are spindle-shaped, tightly packed, and more aggressive. This subtype accounts for 20-35% of malignant pleural mesothelioma cases and behaves based on the ratio of the two cell types, with higher sarcomatoid content linked to faster spread. It most often occurs in the pleura but can appear in the peritoneum, pericardium, or tunica vaginalis.
What does a biphasic tumor mean?
Biphasic refers to a tumor containing two distinct types of cancer cells. In mesothelioma, this means the tumor has both epithelioid cells (cube-shaped, slower-growing, more responsive to treatment) and sarcomatoid cells (spindle-shaped, more aggressive, harder to treat). A diagnosis of biphasic mesothelioma requires at least 10% of both cell types present in the same tumor. Biphasic mesothelioma accounts for 20-35% of all mesothelioma cases and is considered the second most common cell type. Because the two cell types behave differently, treatment response varies among people with biphasic mesothelioma, and prognosis generally depends on the proportion of each cell type present.
What is the most aggressive form of mesothelioma?
Sarcomatoid mesothelioma is the most aggressive form of the disease. It accounts for 10% to 20% of all mesothelioma cases and is characterized by spindle-shaped cells that grow in a spread-out pattern, causing the cancer to advance and metastasize faster than other cell types. People with sarcomatoid mesothelioma often have poorer treatment outcomes, as chemotherapy and radiation are less likely to produce long-term remission compared to other histological subtypes, and surgery may not be recommended. In biphasic mesothelioma (which contains both epithelioid and sarcomatoid cells), prognosis depends on the ratio of cell types, with higher proportions of sarcomatoid cells indicating more aggressive disease.