Ascites in Peritoneal Mesothelioma

Ascites — the pathological accumulation of fluid within the peritoneal cavity — is one of the most common and clinically significant manifestations of peritoneal mesothelioma. Present in an estimated 60-100% of patients at diagnosis, ascites is frequently the symptom that first brings patients to medical attention and ultimately leads to the discovery of underlying malignancy.¹

In peritoneal mesothelioma, ascites develops because malignant mesothelial cells lining the abdominal cavity disrupt normal fluid homeostasis. The tumor produces excess peritoneal fluid through several mechanisms: increased vascular permeability driven by vascular endothelial growth factor (VEGF), lymphatic obstruction preventing normal fluid reabsorption, and direct tumor secretion. As the disease progresses, fluid volumes can exceed several liters, causing significant abdominal distension and discomfort.²

Paracentesis — needle drainage of ascitic fluid — serves both diagnostic and therapeutic purposes. Cytological analysis of the fluid can reveal malignant mesothelial cells, though sensitivity varies (30-75%). Immunohistochemical staining of cell block preparations for markers such as calretinin, WT-1, and CK5/6 improves diagnostic accuracy. Therapeutically, large-volume paracentesis provides significant symptom relief, though fluid typically reaccumulates within days to weeks.³

The volume and distribution of ascites, combined with the extent of peritoneal tumor implants, are assessed using the Peritoneal Cancer Index (PCI) — a scoring system that divides the abdomen into 13 regions and grades tumor burden in each. The PCI score is a critical factor in determining whether a patient is a candidate for cytoreductive surgery with heated intraperitoneal chemotherapy (CRS/HIPEC), the most effective treatment for peritoneal mesothelioma.⁴

Malignant vs. Non-Malignant Ascites

• Malignant ascites — caused by peritoneal surface malignancy (mesothelioma, ovarian cancer, gastrointestinal cancers); typically exudative with high protein and LDH levels; may contain malignant cells on cytology
• Non-malignant ascites — caused by liver cirrhosis (most common), heart failure, nephrotic syndrome, or infections; typically transudative; serum-ascites albumin gradient (SAAG) ≥1.1 g/dL suggests portal hypertension

In peritoneal mesothelioma, ascites is almost exclusively malignant and exudative, with a SAAG <1.1 g/dL.¹

Symptoms related to ascites in peritoneal mesothelioma include:²

• Progressive abdominal distension — the most visible sign; waistline expansion over weeks to months
• Abdominal pain or pressure — dull, diffuse discomfort worsening as fluid accumulates
• Early satiety — feeling full quickly due to compression of the stomach
• Nausea and vomiting — from pressure on abdominal organs
• Dyspnea — difficulty breathing when large fluid volumes push the diaphragm upward
• Weight gain — paradoxical weight increase despite loss of muscle mass and appetite
• Ankle edema — may accompany large-volume ascites

In the context of mesothelioma, ascites results from malignant transformation of peritoneal mesothelial cells following asbestos fiber exposure:¹

• Asbestos fiber migration to the peritoneum — fibers reach the abdominal cavity via the lymphatic system or by traversing the diaphragm
• Tumor-driven fluid production — malignant cells secrete VEGF and other factors increasing vascular permeability
• Lymphatic obstruction — tumor growth blocks normal peritoneal fluid drainage pathways
• Peritoneal surface inflammation — chronic inflammation increases fluid transudation

Diagnostic Evaluation of Ascites

• Paracentesis with cytology — fluid analysis for malignant cells; sensitivity 30-75% for mesothelioma
• Immunohistochemistry — calretinin, WT-1, D2-40, CK5/6 positive; CEA, BerEP4 negative (distinguishes from carcinoma)
• CT abdomen/pelvis with contrast — identifies peritoneal thickening, omental caking, and extent of ascites
• Serum-ascites albumin gradient (SAAG) — <1.1 g/dL in malignant ascites
• Laparoscopy with biopsy — definitive diagnosis when cytology is non-diagnostic
• PCI scoring — performed during surgery to quantify tumor burden across 13 abdominal regions

Management of Ascites in Peritoneal Mesothelioma

• Therapeutic paracentesis — large-volume drainage (up to 5+ liters) for immediate symptom relief; may be repeated as needed
• Diuretics — spironolactone and furosemide may slow fluid reaccumulation in some patients
• Tunneled peritoneal catheter — indwelling catheter for patients requiring frequent drainage
• CRS/HIPEC — cytoreductive surgery with heated intraperitoneal chemotherapy; most effective treatment for eligible patients with PCI ≤20
• Systemic chemotherapy — pemetrexed/cisplatin regimen may reduce ascites by controlling tumor growth
• Intraperitoneal chemotherapy — direct instillation of chemotherapy agents into the peritoneal cavity

The presence of significant ascites generally correlates with advanced peritoneal mesothelioma and higher PCI scores. However, prognosis depends heavily on tumor histology, PCI score, and whether the patient is eligible for CRS/HIPEC. Patients with epithelioid histology who undergo complete cytoreduction with HIPEC have median survival of 40-60 months. For patients managed with palliative care alone, median survival is approximately 6-12 months.⁴

Living with recurrent ascites requires ongoing management. Patients may benefit from a low-sodium diet (limiting fluid retention), regular scheduled paracentesis, monitoring of nutritional status (protein loss through drainage), and coordination with a palliative care team to manage symptoms and maintain quality of life.³