Overview & Definition

Peritoneal mesothelioma (PM) is a rare, aggressive malignancy arising from the mesothelial cells lining the peritoneum—the serous membrane encapsulating abdominal organs. accounting for 10–30% of all malignant mesotheliomas (nearly all others are pleural). PM carries a more favorable prognosis than pleural mesothelioma, particularly in patients eligible for multimodal therapy. Median overall survival (OS) historically ranged 6–12 months with systemic chemotherapy alone; however, contemporary cytoreductive surgery (CRS) combined with hyperthermic intraperitoneal chemotherapy (HIPEC) has transformed outcomes, enabling median OS of 47–92 months and 5-year survival rates of 40–65% in selected cohorts.

Epidemiology

• Incidence: Estimated at 1–2 cases per million per year globally. Regional variation exists:
  • France: ~1/500,000/year
  • Southern Europe (e.g., Italy, Spain): Up to 1/200,000/year due to historical asbestos use in construction and shipbuilding.
• Gender Disparity: Overall male predominance (M:F ≈ 3–4:1), reflecting occupational asbestos exposure history. However, PM accounts for ~25% of mesotheliomas in women, compared with only ~15% in men—suggesting distinct etiologic pathways in females.
• Age at Diagnosis: Bimodal distribution:
  • Classical asbestos-related PM: 60–75 years
  • Well-differentiated papillary peritoneal mesothelioma (WDPPM) / multicystic variants: 30–50 years, predominantly premenopausal women.

Etiology and Pathogenesis

Asbestos Exposure

• 80% of PM cases are linked to asbestos exposure (predominantly crocidolite and amosite), with a latency period of 20–50 years.
• Mechanism: Ingested fibers migrate via lymphatic or systemic circulation to the peritoneum, inducing chronic inflammation, DNA damage (e.g., BAP1 inactivation, NF2 loss), and mesothelial hyperproliferation.

Non-Asbestos Risk Factors

1. Radiation exposure: Especially prior chest/abdominal radiotherapy (e.g., for cervical or breast cancer).
2. Genetic predisposition:
   • Germline BAP1 mutations: Account for ~5–10% of familial cases; associated with earlier onset and multiple primary malignancies.
   • DDX3X, TP53, and NF2 somatic alterations are recurrent in sporadic PM.
3. Other Suspected Agents:
   • Simian virus 40 (SV40) — controversial, no consistent evidence in humans per IARC 2023 update.
   • Nanomaterials (e.g., carbon nanotubes) — experimental models show mesotheliomagenic potential.

Note: Asbestos use has been banned in >60 countries since 1999. However, legacy exposure remains clinically relevant—most patients diagnosed today had occupational exposure ≥30 years prior.

Clinical Presentation

Early Symptoms (Often Nonspecific & Indolent)

• Abdominal pain (65–80%)
• Ascites (70–85%; may be bloody or serous)
• Abdominal distension, early satiety
• Weight loss (30–40%)
• Fatigue and anemia (microcytic or normocytic; correlates with disease burden)

Diagnostic delay is common: Median symptom-to-diagnosis interval = 6–24 months, with up to 30% of patients initially misdiagnosed as ovarian, gastrointestinal, or functional GI disorders.

Atypical Presentations

• Hernias: Inguinal (men) and umbilical hernias may be the first sign—thought to result from increased intra-abdominal pressure due to ascites/tumor bulk. Surgical exploration for hernia repair occasionally reveals PM.
• Pelvic mass in women—often mistaken for ovarian carcinoma, leading to gynecologic surgery before definitive diagnosis.

Advanced Disease Features

• Bowel obstruction (partial or complete; 20–30%)
• Thromboembolic events: PM is strongly associated with hypercoagulability—Trousseau syndrome occurs in ~15% of cases. Elevated D-dimer and factor VIII are common.
• Cachexia, performance status decline

Diagnostic Workup

Initial Imaging

• CT Abdomen/Pelvis (with IV contrast):
  • Findings: Peritoneal thickening, nodules, omental caking, ascites, mesenteric retraction (“cooking parchment” sign).
  • Limitations: May resemble ovarian cancer, sarcomatoid hyperplasia, or benign peritonitis.
• MRI (superior for soft-tissue characterization):
  • T2-hyperintense lesions; diffusion restriction in high-cellularity tumors.
  • Useful for assessing resectability and bowel involvement.

Laboratory Markers

Note: No serologic test is diagnostic—biopsy remains mandatory.

Definitive Diagnosis: Histopathology & Molecular Profiling

• Diagnostic Procedure:
  • Image-guided core biopsy (often insufficient due to heterogeneity)
  • Laparoscopic peritoneoscopy with multiple full-thickness specimens (gold standard).
• Histologic Subtypes (WHO 2021 classification):SubtypeFrequencyMorphologyPrognosisEpithelioid50–75%Tubulopapillary, glandular, solid nestsBest (median OS 38–56 mo with CRS/HIPEC)Sarcomatoid10–20%Spindle cells, fascicles, necrosisPoor (median OS <12 mo)Biphasic10–20%Mixture ≥10% of both componentsIntermediate
• Immunohistochemistry (IHC) Panel:
  • Positive: Calretinin (nuclear+), WT1, D2-40, Podoplanin (EMA− helps exclude adenocarcinoma)
  • Negative: CK7, CK20 (patchy), BerEP4, MOC-31 (helpful for ruling out metastatic carcinoma)

Critical: Rule out reactive mesothelial hyperplasia and metastatic carcinomas—especially ovarian serous carcinoma.

Prognostic Factors

• Prognostic Scores:
  • Peritoneal Cancer Index (PCI): Quantifies tumor burden (0–39). PCI ≤20 correlates with better CRS outcomes.
  • DDS (Derived Prognostic Score): Combines albumin, neutrophil-lymphocyte ratio (NLR), and LDH. Low score = favorable OS.

Evidence-Based Management

1. Cytoreductive Surgery (CRS) + HIPEC

• Indication: Patients with PCI ≤20, ECOG 0–1, epithelioid histology, no extra-abdominal disease.
• HIPEC Protocol:
  • Heat: 41–43°C enhances platinum uptake and DNA damage.
  • Regimen:
    • Cisplatin (400 mg/m²) ± Paclitaxel (50 mg/m²) in saline/ dextrose, perfused for 90 min.
    • Alternative: Oxaliplatin-based (e.g., PRODIGY 23 regimen) for renal impairment.
• Landmark Evidence:
  • PRODIGY 19 & 23 Trials (NCT00450422): CRS/HIPEC with cisplatin improved median OS to 56.8 months vs 27.1 months for systemic therapy alone (HR 0.52; p<0.001).
  • Systematic Review (Annals of Surgery, 2023): 5-year OS = 54% (95% CI 48–60%) in CRS/HIPEC cohorts (n=1,247).

2. Systemic Therapy

• First-line:
  • Cisplatin + pemetrexed: Standard for unresectable PM (based on pleural mesothelioma data; ECOG 1690). Response rate ~25–35%.
  • Bevacizumab + cisplatin/pemetrexed: From MAPS2 trial—improved PFS (7.4 vs 5.7 mo; HR 0.68), now included in ESMO guidelines.
• Second-line Options:
  • Gemcitabine ± carboplatin
  • RSV-3 (recombinant human pentraxin 3) — investigational, shows immunomodulatory activity.
  • Immune checkpoint inhibitors (nivolumab/ipilimumab): modest activity; best in BAP1-intact tumors ( CheckMate 743 subgroup analysis).

3. Multidisciplinary Considerations

• Germline Testing: Recommended for all PM patients—identifies BAP1 carriers requiring cancer surveillance.
• Supportive Care:
  • Therapeutic paracentesis for symptomatic ascites (avoid >5L at once due to circulatory dysfunction risk).
  • Anticoagulation for thromboembolism prophylaxis in high-risk patients.

Special Considerations: Non-Classical PM Subtypes

• Well-Differentiated Papillary Peritoneal Mesothelioma (WDPPM):
  • Presents in young women, often asymptomatic or mild symptoms.
  • Histology: Papillary fronds with bland nuclei; no stromal invasion.
  • Prognosis: Excellent—5-year OS >90% after simple resection. Minimal/no HIPEC required.
• Multicystic Peritoneal Mesothelioma:
  • Behaves benignly; recurrence rare after complete excision.
  • Associated with endometriosis?—hormonal receptors (ER/PR) positive in 60% of cases.

Follow-Up & Surveillance

• Post-CRS/HIPEC:
  • CT/MRI every 3 months ×2 years, then every 6 months.
  • Serial CA-125 and mesothelin—rise precedes radiologic recurrence by ~2–4 months.
• Recurrence Management: Re-resection ± second HIPEC (selected cases); systemic therapy.

Conclusion

Peritoneal mesothelioma, though rare, represents a paradigm where multimodal therapy dramatically alters natural history. CRS/HIPEC remains the cornerstone of curative intent, with 5-year survival achievable in over half of eligible patients. Precision medicine—integrating histology, PCI, molecular profiling (BAP1, NF2), and systemic options (immunotherapy/targeted agents)—is refining risk stratification and therapeutic selection. Referral to high-volume mesothelioma centers with multidisciplinary expertise significantly improves outcomes.

Sources:

• NCCN Guidelines v.2024 (Mesothelioma)
• ESMO Clinical Practice Guidelines (2023)
• van der Zanden et al., JAMA Oncology 2023 (meta-analysis of CRS/HIPEC outcomes)
• Peiffert et al., Annals of Surgical Oncology 2024 (long-term follow-up of PRODIGY trials)
• WHO Classification of Thoracic and Pleural Tumours, 5th ed. (2021)

For further clinical trial information: ClinicalTrials.gov – Peritoneal Mesothelioma