Peritoneal Mesothelioma

Peritoneal Mesothelioma
Also Known As	Malignant Peritoneal Mesothelioma (MPM)
Location	Peritoneum (abdominal lining)
Annual US Cases	~800 new cases per year
Percentage of Meso	7–30% of all mesothelioma
Median Survival (HIPEC)	~53 months
5-Year Survival	30–50% with optimal treatment
Peak Latency	20–50 years

Peritoneal Mesothelioma

Malignant peritoneal mesothelioma (MPM) is a rare, aggressive cancer arising from the mesothelial cells lining the peritoneum — the membrane surrounding the abdominal cavity and organs. It is the second most common form of mesothelioma after pleural mesothelioma, accounting for approximately 7–30% of all diagnoses. Approximately 800 new cases are diagnosed in the United States each year.

Unlike pleural mesothelioma, peritoneal mesothelioma has a near-equal male-to-female ratio and a meaningful proportion of cases (20–40%) occur in patients without documented asbestos exposure. The disease has been transformed by the development of cytoreductive surgery combined with hyperthermic intraperitoneal chemotherapy (CRS/HIPEC), which has extended median survival from approximately 12 months to 53 months or more in selected patients.

Overview

Definition and Incidence

Peritoneal mesothelioma develops in the peritoneum, the serosal membrane lining the abdominal cavity and covering the abdominal organs. The disease remains rare, with an age-adjusted incidence rate of approximately 1.02 cases per 1,000,000 person-years in the United States based on SEER data from 2000–2018. US incidence has remained broadly stable over that period, though unadjusted case counts increased by 64.9% driven primarily by new diagnoses in women.

Demographics

Peritoneal mesothelioma differs meaningfully from pleural mesothelioma in patient demographics:

• Male-to-female ratio: Approximately 1.2:1 — dramatically more balanced than pleural mesothelioma's 4:1 male predominance
• Median age at diagnosis: 50–65 years
• Race/ethnicity: White patients account for approximately 75% of cases in SEER data
• Female representation in surgical series: Some CRS/HIPEC centers report that women comprise 59% of operated patients

Women with peritoneal mesothelioma consistently demonstrate superior outcomes after treatment, with 5-year survival rates of 68% in women versus 39% in men.

Asbestos Attribution

Asbestos is the primary known cause of peritoneal mesothelioma, but the attribution rate is lower than for pleural disease. Approximately 60–80% of peritoneal mesothelioma cases have documented asbestos exposure, meaning 20–40% of patients have no identifiable occupational or environmental asbestos contact. By contrast, approximately 96% of pleural mesothelioma cases are attributable to asbestos. The weaker attribution in peritoneal cases reflects a higher proportion of female patients with secondary (paraoccupational) exposure, a greater role for BAP1 germline mutations, and incomplete occupational histories.

Symptoms and Diagnosis

Symptom Profile

Peritoneal mesothelioma presents with non-specific abdominal symptoms that frequently delay diagnosis by a median of 4–6 months from initial presentation. The most common presenting symptoms include:

• Abdominal distension and bloating — occurring in over 30–50% of patients
• Abdominal pain — occurring in over 30–50% of patients
• Ascites (fluid accumulation) — often the presenting clinical finding
• Weight loss and early satiety
• Nausea, fatigue, and altered bowel habits
• New-onset hernia or palpable abdominal mass (less common)

Due to these non-specific symptoms, peritoneal mesothelioma is frequently misdiagnosed as ovarian cancer in women, irritable bowel syndrome, or peritoneal carcinomatosis from other primary cancers such as stomach, pancreas, or colon.

Key Facts: Peritoneal Mesothelioma at a Glance

Fact	Data
Annual US cases	~800 new diagnoses per year
Share of all mesothelioma	7–30% (most cited: 10–20%)
Male-to-female ratio	~1.2:1 (near-equal)
Cases with no asbestos exposure	20–40%
Median age at diagnosis	62–65 years
Latency period	20–50 years from first exposure
Median survival (untreated)	~6 months
Median survival (chemo alone)	~12 months
Median survival (CRS/HIPEC)	~53 months
5-year survival (CRS/HIPEC)	41–59%
Trust fund compensation range	$7,000–$1.2 million per fund
Average lawsuit settlement	$1 million–$1.4 million

Diagnostic Imaging

CT scan of the chest, abdomen, and pelvis is the initial imaging modality of choice. Favorable CT findings include ascites with minimal soft-tissue masses and preserved bowel architecture. Unfavorable CT findings include large nodular thickening with marked bowel distortion, which predicts incomplete cytoreduction.

MRI with diffusion-weighted imaging can predict the peritoneal cancer index (PCI) preoperatively with good accuracy. FDG-PET/CT demonstrates uptake along the peritoneum but has unclear utility for initial staging.

Tissue Biopsy and Immunohistochemistry

Diagnostic laparoscopy with biopsy is the preferred approach to obtain tissue, as it allows simultaneous visualization of tumor burden and PCI assessment. Paracentesis and cytology of ascitic fluid has limited diagnostic yield and is not recommended as a sole approach.

A panel of immunohistochemical markers is required to confirm diagnosis. Positive mesothelial markers include calretinin, cytokeratin 5/6, WT-1, and D2-40. Negative markers used to exclude adenocarcinoma include BerEP4, CEA, and TTF-1. Loss of BAP1 nuclear expression is highly specific for distinguishing malignant from benign mesothelial proliferation.

Peritoneal Cancer Index (PCI) Scoring

The Peritoneal Cancer Index (PCI) is the standard tool for quantifying disease burden, dividing the abdomen into 13 regions and assigning each a lesion-size score of 0–3. The maximum PCI score is 39. PCI correlates directly with prognosis and surgical eligibility:

• PCI 1–10 (Stage I): 5-year overall survival 87%
• PCI 11–20 (Stage II): 5-year overall survival 53%
• PCI ≤19: Associated with improved overall survival (p = 0.001)
• PCI ≥30: Associated with significantly worse survival (p = 0.002)

Treatment Options

Peritoneal mesothelioma treatment has advanced substantially over the past two decades. The current standard of care for eligible patients combines cytoreductive surgery (CRS) with hyperthermic intraperitoneal chemotherapy (HIPEC). For patients who cannot undergo surgery, systemic chemotherapy and emerging immunotherapy approaches are available. For information on related options, see treatment options and clinical trials.

Cytoreductive Surgery and HIPEC

CRS/HIPEC is the established standard of care for selected patients with peritoneal mesothelioma and represents the most significant advance in treatment of this disease.

The procedure involves two phases. First, cytoreductive surgery removes all visible tumor through peritonectomies (excision of affected peritoneal surfaces) and visceral resections as needed. A complete parietal peritonectomy is often performed because up to 54% of normal-appearing peritoneum may harbor microscopic disease. Second, immediately following surgery, heated chemotherapy (cisplatin, at 41–42°C) is circulated directly within the abdominal cavity for 60–90 minutes to address microscopic residual disease.

Completeness of cytoreduction (CC score) is the strongest independent predictor of survival. CC-0 (no residual disease) and CC-1 (residual tumor less than 2.5 mm) are achieved in approximately 67% of patients and are associated with the best outcomes. CC-2 and CC-3 scores are associated with significantly worse survival, and HIPEC provides no benefit in patients with suboptimal cytoreduction.

Key outcomes data from major studies:

• Yan et al. multi-institutional study (401 patients, 29 centers): Median overall survival 53 months; 5-year survival 47%
• Helm et al. meta-analysis (1,047 patients, 20 publications): 5-year survival 42%
• Feldman et al. (NCI) (49 patients): Median survival 92 months; 5-year survival 59%
• Sugarbaker multimodality (CRS+HIPEC+NIPEC): Approximately 80% 5-year survival in selected patients

Systemic Chemotherapy

Pemetrexed plus cisplatin is the standard first-line systemic regimen for patients with surgically unresectable peritoneal mesothelioma. Response rates are 25–36%, with median survival of approximately 12.1–13.1 months and disease control rates of approximately 71%. Systemic chemotherapy is primarily used as palliative therapy or as a strategy to assess tumor biology before considering surgical referral — though evidence suggests better outcomes when chemotherapy is given after rather than before CRS/HIPEC.

Immunotherapy

The CheckMate 743 trial, which established nivolumab plus ipilimumab as a first-line standard for pleural mesothelioma, enrolled very few peritoneal patients (18 of 571 total), preventing meaningful subgroup analysis. However, accumulating real-world evidence supports immunotherapy activity in peritoneal mesothelioma:

• A 2025 French real-world cohort of 22 unresectable peritoneal mesothelioma patients treated with immune checkpoint inhibitors demonstrated median progression-free survival of 10 months and median overall survival of 16.8 months, with an objective response rate of 30%.
• A 2024 case report documented a major sustained response to first-line nivolumab plus ipilimumab in a patient with BAP1 loss.
• The NCI Phase II trial (NCT05041062) is actively investigating perioperative nivolumab plus ipilimumab combined with CRS/HIPEC for resectable disease.

BAP1 loss is associated with a more inflamed tumor microenvironment, potentially predicting immunotherapy responsiveness.

PIPAC (Emerging Minimally Invasive Approach)

Pressurized IntraPeritoneal Aerosol Chemotherapy (PIPAC) delivers chemotherapy as a pressurized aerosol into the abdominal cavity during minimally invasive laparoscopy. PIPAC serves two roles: palliative treatment for patients ineligible for CRS/HIPEC, and downstaging therapy to convert initially unresectable disease (PCI >30) to resectable disease. A 2025 case series reported two patients with PCI >30 successfully downstaged by PIPAC to achieve complete cytoreduction at subsequent surgery. The ISSPP PIPAC database (2020–2024) encompassed 3,224 treatments in 1,126 patients with a major complication rate of only 0.7%.

Prognosis and Survival

Peritoneal mesothelioma treated with CRS/HIPEC has a substantially better prognosis than pleural mesothelioma. Population-based overall median survival is approximately 11.6 months, but this reflects many patients who do not undergo surgical treatment. With optimal CRS/HIPEC, peritoneal mesothelioma 5-year survival (47%) far exceeds the approximately 5% 5-year survival typically reported for pleural mesothelioma.

For survival statistics across mesothelioma types, see the linked reference page.

Survival by Histologic Subtype

Histologic subtype is a critical prognostic determinant:

• Epithelioid (79–91% of surgical cases): Best prognosis; independently associated with improved survival on multivariate analysis
• Sarcomatoid (~3% of cases): Most aggressive; median survival 2.0 months in population-based data
• Biphasic (~4% of cases): Intermediate prognosis; hazard ratio 1.49 relative to epithelioid
• Well-differentiated papillary mesothelioma (WDPM): Low malignant potential; most patients survive for years to decades without aggressive treatment

Key Prognostic Factors

Factors independently associated with improved survival include: epithelioid histology, complete cytoreduction (CC-0 or CC-1), female sex, younger age, PCI below 15–17, absence of lymph node metastasis, and use of cisplatin-based HIPEC (versus mitomycin C). A normal preoperative CA-125 level (35 U/mL or below) is associated with 5-year survival of 82% versus 42% with elevated CA-125.

Long-term survival is well-documented. Repeat CRS/HIPEC for recurrence yields approximately 46% 5-year survival.

Asbestos Exposure and Causes

How Asbestos Reaches the Peritoneum

The mechanism by which asbestos fibers reach the peritoneum is not fully established. Three pathways are proposed:

1. Ingestion via mucociliary clearance: Inhaled fibers trapped in the airways are cleared upward, swallowed, and enter the gastrointestinal tract, where they may penetrate through the gut wall into the peritoneum
2. Diaphragmatic translocation: Fibers in the pleural space migrate through diaphragmatic lymphatics or stomata into the peritoneal cavity
3. Hematogenous/lymphatic spread: Fibers may reach abdominal sites via the bloodstream or lymphatic system

Asbestos fibers have been found in the omentum and mesentery of patients with peritoneal mesothelioma, supporting the GI ingestion pathway. Once lodged in the peritoneum, fibers cause chronic inflammation, chromosomal instability, and ultimately malignant transformation of mesothelial cells.

Latency Period

The latency period from initial asbestos exposure to peritoneal mesothelioma diagnosis is typically 20–50 years, though some cases — particularly those associated with BAP1 germline mutations — may present after only 8–10 years. The average age at diagnosis is 62–65 years, reflecting decades of latent disease development.

Non-Asbestos Risk Factors

A meaningful minority of peritoneal mesothelioma cases occur without asbestos exposure. Known or proposed non-asbestos risk factors include:

• BAP1 germline mutations: Present in approximately 12% of mesothelioma patients; significantly increases susceptibility and can dramatically shorten latency
• Prior abdominal radiation therapy
• Chronic peritoneal inflammation (e.g., Mediterranean familial fever)
• Secondary/paraoccupational exposure in women: Laundering contaminated work clothing, physical contact with exposed family members, and household dust are primary exposure routes for many female patients

Occupational Exposure Groups

Workers at historically elevated peritoneal mesothelioma risk include asbestos miners and millers, insulation workers, shipyard workers, pipe fitters, boilermakers, and construction tradespeople exposed to asbestos-containing products. Asbestos fibers have also been found in the omentum of patients whose only documented exposure was secondary or environmental. See the corporate concealment page for historical context on industry knowledge of asbestos risks.

Legal Rights and Compensation

Patients diagnosed with peritoneal mesothelioma have the same legal rights to compensation as those with pleural mesothelioma, though the legal pathway may present additional complexities due to the lower asbestos attribution rate.

⚠ Statute of Limitations Warning: Filing deadlines vary by state from 1-6 years from diagnosis. Texas allows 2 years from diagnosis or discovery. Contact an attorney immediately to preserve your rights.

Asbestos Trust Funds

More than 60 asbestos bankruptcy trusts hold an estimated $25–30 billion available for qualified claimants. Individual trust payments range from $7,000 to $1.2 million per trust, with patients typically filing claims against multiple trusts. The average total recovery across all trust funds is approximately $300,000–$400,000. Peritoneal mesothelioma patients are eligible for trust fund claims on the same basis as pleural mesothelioma patients. For more information on filing, see asbestos trust funds and trust fund claims.

Lawsuits and Verdicts

Average mesothelioma lawsuit settlements fall between $1 million and $1.4 million. Trial verdicts average approximately $2.4 million, with notable cases far exceeding these averages — a 2022 California jury awarded $53.3 million to a mesothelioma patient, and a 2025 Boston jury awarded $8 million to a woman whose disease was linked to talcum powder use. Patients may pursue both trust fund claims and personal injury lawsuits simultaneously to maximize total compensation. See the claims process and statute of limitations pages for state-specific filing deadlines.

Unique Legal Challenges

Peritoneal mesothelioma cases present distinctive legal challenges. Defense attorneys may argue that the lower asbestos attribution rate (60–80% versus 96% for pleural) weakens the causal link. Female plaintiffs with secondary exposure claims, patients with BAP1 mutations, and patients with shorter latency periods all face potential challenges to causation arguments. Experienced mesothelioma attorneys address these challenges through expert medical testimony, occupational and residential exposure history, epidemiological studies of dose-response relationships, and — where relevant — fiber burden analysis and genetic testing evidence.

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• Peritoneal mesothelioma patient resources — Mesothelioma.net

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Frequently Asked Questions

What is peritoneal mesothelioma?

Peritoneal mesothelioma is a cancer of the peritoneum — the thin membrane lining the abdominal cavity and covering the abdominal organs. It is caused primarily by asbestos fiber ingestion or fiber translocation from the pleural space and accounts for approximately 7–30% of all mesothelioma diagnoses. Approximately 800 new cases are diagnosed in the United States each year.

How is peritoneal mesothelioma different from pleural mesothelioma?

Peritoneal mesothelioma develops in the abdominal lining rather than the lung lining, presents with abdominal symptoms (ascites, bloating, pain) rather than chest symptoms, has a near-equal male-to-female ratio (versus 4:1 male predominance in pleural disease), and is more amenable to surgical treatment via CRS/HIPEC. When optimally treated, peritoneal mesothelioma has a substantially better prognosis — 47% 5-year survival with CRS/HIPEC versus approximately 5% for pleural mesothelioma.

What is HIPEC and who is eligible?

HIPEC (hyperthermic intraperitoneal chemotherapy) is a treatment in which heated chemotherapy is circulated directly inside the abdominal cavity immediately after cytoreductive surgery removes all visible tumor. The heat enhances chemotherapy penetration and helps kill microscopic residual cancer cells. Candidates generally have a PCI score below 20, epithelioid or biphasic histology, adequate performance status, and preserved small bowel anatomy. All potentially eligible patients should be evaluated by a peritoneal surface oncology specialist at a high-volume center.

What is the survival rate for peritoneal mesothelioma?

Survival varies significantly by treatment. Without treatment, median survival is approximately 6 months. With systemic chemotherapy alone, median survival is approximately 12 months. With CRS/HIPEC, median survival is 34–92 months (averaging around 53 months in the largest multi-institutional study), and 5-year survival rates of 41–59% have been reported at major centers. Patients with epithelioid histology, low PCI scores, and female sex have the best outcomes.

Can you get compensation for peritoneal mesothelioma without a documented asbestos exposure?

Yes. Even when a patient cannot identify a specific occupational exposure, compensation may still be recoverable. Secondary (paraoccupational) exposure — such as from laundering contaminated clothing or household asbestos dust — is a recognized legal basis for claims. BAP1 germline mutations combined with any level of asbestos exposure can establish causation. Approximately 20–40% of peritoneal mesothelioma cases lack documented occupational exposure, and experienced mesothelioma attorneys are accustomed to building these cases. Contact a qualified mesothelioma attorney to evaluate your specific circumstances.