Definition/General
Introduction:
Malignant peritoneal effusion contains neoplastic cells in ascitic fluid
Results from peritoneal carcinomatosis or primary peritoneal malignancy
Represents advanced stage disease in most cases
Poor prognostic indicator
Requires immediate oncological management.
Origin:
Results from hematogenous spread to peritoneum
Direct extension from intra-abdominal organs
Transcoelomic spread via peritoneal cavity
Primary peritoneal carcinoma
Lymphatic dissemination
Implantation during surgery.
Classification:
Classified as exudative ascites
SAAG <1.1 g/dL
High protein content >2.5 g/dL
Elevated tumor markers
Based on primary site: ovarian, gastric, pancreatic, colorectal
Primary vs secondary peritoneal malignancy.
Epidemiology:
Accounts for 10-15% of all ascites
Most common in ovarian (60%) and GI malignancies (30%)
Female predominance (ovarian primary)
Peak incidence 50-70 years
Poor prognosis with median survival 6-12 months.
Clinical Features
Presentation:
Progressive abdominal distention
Early satiety and bloating
Abdominal pain or discomfort
Nausea and vomiting
Dyspnea due to diaphragmatic elevation
Weight loss despite fluid accumulation.
Symptoms:
Abdominal distention (90% cases)
Early satiety (80% cases)
Abdominal pain (70% cases)
Nausea and vomiting (60% cases)
Dyspnea (50% cases)
Leg swelling (40% cases)
Fatigue and weakness (85% cases).
Risk Factors:
Previous malignancy history
Family history of ovarian/breast cancer
BRCA1/2 mutations
Advanced age
Nulliparity (ovarian cancer)
Chronic inflammatory conditions.
Screening:
Tumor markers: CA-125, CEA, CA 19-9
CT abdomen and pelvis
Ultrasound abdomen
Cytological examination of ascitic fluid
Image-guided biopsy if needed.
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Gross Description
Appearance:
Malignant ascites is often hemorrhagic or serosanguineous
Turbid to cloudy appearance
May be yellow to brown
Viscous consistency due to high protein
Large volume typically present.
Characteristics:
High protein content >2.5 g/dL
Elevated LDH >200 U/L
SAAG <1.1 g/dL
Low glucose may be present
Elevated tumor markers
pH may be acidic.
Size Location:
Massive ascites often present
Loculated due to adhesions and tumor deposits
Omental involvement common
Peritoneal studding
Pelvic masses may be palpable.
Multifocality:
Widespread peritoneal involvement
Omental caking
Multiple peritoneal implants
Retroperitoneal lymphadenopathy
Liver surface involvement.
Microscopic Description
Histological Features:
Malignant cells in clusters, papillary fragments, and single cells
High cellularity >1000 cells/μL
Pleomorphic malignant cells
High nuclear-cytoplasmic ratio
Mitotic activity
Necrotic background.
Cellular Characteristics:
Large pleomorphic cells
Hyperchromatic nuclei with irregular contours
Prominent nucleoli
Increased nuclear-cytoplasmic ratio
Cytoplasmic vacuoles (adenocarcinoma)
Signet ring cells (gastric primary).
Architectural Patterns:
Three-dimensional cell clusters
Papillary architecture (ovarian/peritoneal)
Acinar formations (adenocarcinoma)
Single cell pattern (lobular breast cancer)
Sheet-like arrangement
Psammoma bodies (serous carcinoma).
Grading Criteria:
Nuclear grading: Grade 1 (mild atypia)
Grade 2 (moderate atypia)
Grade 3 (severe atypia)
Mitotic count
Architectural complexity
Necrosis presence.
Immunohistochemistry
Positive Markers:
Primary site-specific markers
Ovarian: WT1, PAX8, CA-125
Breast: GATA3, mammaglobin, GCDFP-15
GI tract: CDX2, CK20
Pancreas: CA 19-9, DPC4 loss
Lung: TTF-1, napsin A.
Negative Markers:
Calretinin, WT1 (to exclude reactive mesothelial)
Site-specific negatives
CK5/6 usually negative in adenocarcinoma
p63 negative in most adenocarcinomas.
Diagnostic Utility:
Essential for primary site identification
Adenocarcinoma vs mesothelioma differentiation
Panel approach recommended
CK7/CK20 pattern helpful
ER/PR for breast/gynecologic primaries.
Molecular Subtypes:
Based on primary site and histology
High-grade serous (ovarian)
Mucinous adenocarcinoma
Signet ring cell carcinoma
Clear cell carcinoma
Neuroendocrine carcinoma.
Molecular/Genetic
Genetic Mutations:
TP53 mutations (high-grade serous)
KRAS mutations (pancreatic, colorectal)
BRCA1/2 mutations (ovarian, breast)
PIK3CA mutations
ARID1A mutations (clear cell, endometrioid).
Molecular Markers:
Tumor markers elevated: CA-125, CEA, CA 19-9
AFP (hepatocellular, germ cell)
Beta-hCG (choriocarcinoma)
Inhibin (granulosa cell tumor)
Chromogranin, synaptophysin (neuroendocrine).
Prognostic Significance:
Stage IV disease indicator
Poor prognosis overall
Primary site affects survival
Response to chemotherapy variable
Platinum sensitivity (ovarian)
Targeted therapy options emerging.
Therapeutic Targets:
Chemotherapy based on primary site
Targeted therapy: HER2, EGFR, VEGF
PARP inhibitors (BRCA-mutated)
Immunotherapy (MSI-high tumors)
Palliative paracentesis.
Differential Diagnosis
Similar Entities:
Reactive mesothelial proliferation
Malignant mesothelioma
Lymphoma (primary effusion)
Metastatic carcinoma from different primaries
Primary peritoneal carcinoma.
Distinguishing Features:
Malignancy: Cytological atypia
Malignancy: Architectural complexity
Reactive: Bland nuclear features
Mesothelioma: Calretinin positive
Lymphoma: Lymphoid markers positive
Primary site: Specific IHC patterns.
Diagnostic Challenges:
Distinguishing from reactive mesothelial proliferation
Primary site identification
Low-grade malignancies may be subtle
Processing artifacts
Sampling adequacy.
Rare Variants:
Primary peritoneal carcinoma
Mesothelioma
Lymphomatosis
Germ cell tumors
Sarcomatous malignancies
Neuroendocrine carcinoma.
Sample Pathology Report
Template Format
Sample Pathology Report
Complete Report: This is an example of how the final pathology report should be structured for this condition.
Specimen Information
Peritoneal fluid, volume [X] mL, [appearance - hemorrhagic/turbid/cloudy]
Adequacy
Adequate for cytological evaluation
Cellularity
High cellularity with [X] cells/μL
Malignant Cells
POSITIVE for malignant cells
Morphological Features
Malignant cells present in [clusters/single cells/papillary fragments]. Cells show [nuclear features] with [cytoplasmic features]. [Architectural pattern] noted.
Cell Type
Morphology consistent with [adenocarcinoma/other carcinoma type]
Immunohistochemistry
IHC panel: [List positive and negative markers]
Primary Site Assessment
IHC pattern suggests [primary site/unknown primary]
Final Diagnosis
MALIGNANT peritoneal effusion - [Carcinoma type] consistent with [primary site/unknown primary]
Comment
Findings indicate peritoneal carcinomatosis. Clinical correlation with imaging and tumor markers recommended. Oncology consultation advised.