Peritoneal vs Pleural Mesothelioma: A 2026 Data Comparison

Mesothelioma is often described as a single disease, but the data tells a different story. Where the cancer starts in the body changes nearly everything about it: how common it is, how it is treated, how long people live with it, and how their immune systems respond.

Pleural mesothelioma and peritoneal mesothelioma share a cause (asbestos exposure) and a cell of origin (mesothelial cells lining body cavities), but clinically they behave like different diseases. A 2026 preclinical study in Scientific Reports made the biology of that difference explicit. The data below compares the two side by side.

Side-by-Side Comparison

Incidence: Why Pleural Dominates

Of the approximately 3,000 mesothelioma cases diagnosed annually in the United States, pleural disease accounts for the large majority. SEER data and published epidemiological studies put the pleural share at 68% to 85%, with peritoneal at 9% to 24% and rare sites (pericardial, tunica vaginalis testis) accounting for less than 5%.

The difference reflects how asbestos reaches the body. Inhaled fibers lodge in the lung lining, where the pleura is exposed to every breath. Fibers can also travel through the lymphatic system and deposit in the abdominal cavity, which is how peritoneal mesothelioma develops, but this route is less efficient.

The demographics differ slightly as well. Pleural mesothelioma is overwhelmingly male (about 80%) because of occupational exposure patterns in industries like shipbuilding, construction, and asbestos manufacturing. Peritoneal mesothelioma shows a higher proportion of women, with some studies reporting the female share approaching 40%.

Survival: The Counterintuitive Pattern

Despite being the rarer and historically less-studied form, peritoneal mesothelioma has better overall survival than pleural disease.

Median overall survival for peritoneal mesothelioma is approximately 33 months, compared to 13 months for pleural disease. Five-year survival for peritoneal patients treated at high-volume centers with cytoreductive surgery and HIPEC can reach 47% to 52%. Five-year survival for pleural patients on first-line immunotherapy is approximately 14%.

The gap exists for two main reasons.

First, peritoneal mesothelioma is more amenable to complete surgical removal. Because the abdominal cavity is a single compartment, surgeons can often remove all visible tumor during a cytoreductive surgery, then bathe the cavity in heated chemotherapy (HIPEC) to kill microscopic disease. This approach, pioneered at specialized centers, has transformed peritoneal outcomes since the early 2000s.

Second, peritoneal mesothelioma tends to stay localized longer. Pleural disease often spreads beyond the chest cavity earlier in its course, making complete resection harder and driving reliance on systemic therapy.

Treatment Approaches Diverge

The standard of care for the two diseases has evolved in different directions.

Pleural mesothelioma is treated as a systemic disease in most cases. First-line immunotherapy (nivolumab plus ipilimumab) has been the standard since 2020, extending median survival from 14 to 18 months in the CheckMate-743 trial. A subset of patients with early-stage, epithelioid disease may be candidates for multimodal therapy combining surgery, chemotherapy, and radiation.

Peritoneal mesothelioma treatment centers on cytoreductive surgery with HIPEC for operable patients. The approach produces 5-year survival rates of 47% to 52% in appropriate candidates, making it the most effective treatment for any form of mesothelioma. For patients whose disease cannot be surgically removed, systemic options are more limited. No immunotherapy has been specifically approved for peritoneal disease.

The Immune Environment Is Different

A 2026 preclinical study in Scientific Reports (Nature) mapped the biological differences between pleural and peritoneal mesothelioma at the level of the tumor microenvironment. Researchers at the Harry Perkins Institute in Australia implanted identical mesothelioma cell lines in three locations in mice and measured the immune response.

The pleural cavity produced an inflammatory environment with strong interferon signaling, high T cell and NK cell infiltration, and gene signatures linked to immunotherapy response.

The peritoneal cavity produced the opposite. Tumors in the abdomen showed low interferon signaling, fewer T cells, and dominance by macrophages. The gene expression profile matched signatures of checkpoint therapy resistance.

When the researchers treated the tumors with immune checkpoint therapy, the pattern held. Pleural and subcutaneous tumors responded. Peritoneal tumors did not. The same cell line, the same treatment, different results based on location alone.

The finding helps explain a longstanding clinical observation: checkpoint therapy trials in peritoneal mesothelioma have produced modest results. A retrospective study of 24 patients treated with pembrolizumab reported only a 21% partial response rate. Individual case reports describe dramatic responses, but prospective controlled data remain scarce.

Why It Matters for Treatment Planning

The pleural-peritoneal distinction should guide treatment decisions in ways that are still underused in clinical practice.

For pleural patients, checkpoint therapy is a proven first-line option and the only FDA-approved immunotherapy regimen. Clinical trials focus overwhelmingly on this subtype.

For peritoneal patients, cytoreductive surgery with HIPEC should be considered first whenever feasible. Referral to a peritoneal surface malignancy center is important because outcomes depend heavily on surgical skill and center volume.

For unresectable disease, clinical trial enrollment is often the best path to newer therapies. Bispecific antibodies like BNT327 showed a 75% response rate in peritoneal patients in Phase 2 data.

Patients with peritoneal mesothelioma should ask specifically whether a clinical trial is available, because most landmark immunotherapy trials (CheckMate-743, DREAM, PrE0505) have explicitly excluded them.

What the Data Still Does Not Tell Us

Several gaps remain in the comparison.

Most immunotherapy trials have excluded peritoneal patients, so head-to-head comparisons of checkpoint therapy between the two subtypes rely on retrospective and single-arm data.

Long-term survival data for peritoneal mesothelioma treated outside of HIPEC-capable centers is limited. Real-world outcomes for the many peritoneal patients who never reach a specialized center may be lower than the published 47% to 52% five-year figures.

Biomarkers that predict response to treatment are poorly developed in both subtypes. PD-L1 expression, widely used in other cancers, correlates weakly with outcomes in pleural mesothelioma and has not been prospectively validated in peritoneal disease.