What is the diagnostic workup and treatment approach for a patient suspected of having peritoneal carcinomatosis with a history of previous cancer diagnoses?

Diagnostic Workup for Peritoneal Carcinomatosis

For patients with suspected peritoneal carcinomatosis and prior cancer history, begin with serum tumor markers (CA-125, CEA, CA19-9) and contrast-enhanced CT of chest/abdomen/pelvis, followed by diagnostic laparoscopy with peritoneal cytology for definitive confirmation in surgical candidates. 1

Initial Clinical Assessment

• Obtain detailed history of previous malignancy, as the most common primary origins are breast, colon, gastric, pancreatic, and ovarian cancer 1
• In young women, measure alpha-fetoprotein and beta-HCG to exclude germ cell tumors 1
• Perform physical examination focusing on ascites, abdominal distention, pelvic masses, and supraclavicular lymphadenopathy 2

Serum Tumor Markers (First-Line)

• Measure CA-125 before any intervention 1
• If CA-125 is normal, obtain CA19-9 and CEA 1
• These markers guide differential diagnosis and help identify the primary tumor origin 1

Imaging Studies: Sequential Algorithm

First-Line: Ultrasound

• Ultrasound detects peritoneal carcinomatosis with high specificity: omental involvement in 97% of cases, peritoneal implants in 54%, and serosal involvement in 19% 1
• Useful for initial evaluation but has limited sensitivity for small-volume disease 3

Second-Line: Contrast-Enhanced CT

• CT of thorax, abdomen, and pelvis with IV and oral contrast is the standard imaging modality due to availability, cost-effectiveness, and relatively high sensitivity 1, 4
• Critical limitation: CT sensitivity for detecting peritoneal carcinomatosis is only 28-51%, though specificity is high at 97-99% 1, 4
• Look for three cardinal findings: ascites, nodular peritoneal implants, and infiltration of peritoneal fatty tissue 3
• Enhanced abdominal/pelvic CT is specifically recommended for diagnosis of ovarian metastases and peritoneal metastases in colorectal cancer 2

Third-Line: MRI

• Consider MRI when CT findings are equivocal or for better characterization of liver metastases 2
• Sensitivity comparable to CT for implants >10mm 3
• Diffusion-weighted imaging (DWI) improves detection of small peritoneal deposits 2

PET-CT: Limited Role

• PET-CT is NOT routinely recommended 2, 4
• Sensitivity for detecting peritoneal carcinomatosis is only 3% compared to 85% for laparoscopy 1
• May be useful only when clinical suspicion exists but other imaging is negative, or before major treatment decisions 2
• Particularly limited in mucinous or diffuse tumors due to lower tracer uptake 2, 4

Definitive Diagnostic Confirmation

Laparoscopy with Peritoneal Cytology (Gold Standard)

• Diagnostic laparoscopy is the standard indication for all potentially resectable stage IB-III gastric cancers and high-risk cases where CT is doubtful 2, 1
• Sensitivity of 85% and specificity of 100% for detecting peritoneal carcinomatosis not identified by imaging 1
• Global sensitivity for detecting peritoneal metastases is 84.6% with specificity of 100% 2, 1
• Perform peritoneal washings for cytology in all cases 2
• Document disease burden using the Peritoneal Cancer Index (PCI), which divides the abdomen into 13 regions scored 0-3 based on lesion size 2, 4

Tissue Acquisition for Histological Diagnosis

Paracentesis (if ascites present):

• Paracentesis with cytological analysis is the initial standard when ascites is present 1
• Sensitivity of 96.7% if three samples are sent immediately 1
• Cytology is positive only in peritoneal carcinomatosis, not in hepatic or lymph node metastases without peritoneal involvement 1

Peritoneal biopsy:

• Peritoneal biopsies alone are insufficient for definitive diagnosis 1
• Require representative samples of adequate size, ideally including primary tumor tissue when possible 1

Peritoneal Cancer Index (PCI) Documentation

• Quantify disease burden by scoring each of 13 abdominal regions from 0-3 based on lesion size (total score 0-39) 4
• PCI ≤10 indicates limited disease suitable for cytoreductive surgery plus HIPEC in selected malignancies 4
• PCI ≥20 indicates extensive disease burden but is not an absolute contraindication to surgery 4
• Lower PCI scores are associated with better prognosis 2

Differential Diagnosis Considerations

• Rule out tuberculous peritonitis, which requires tissue biopsy showing caseating granulomas and acid-fast bacilli (diagnostic yield 84-100%) 1
• Exclude primary peritoneal malignancies, endometriosis, and other inflammatory/infectious diseases 3
• In women with pelvic masses, rule out bowel, uterine, pancreatic cancers and lymphoma 2

Common Diagnostic Pitfalls to Avoid

• Do not rely solely on CT for preoperative staging due to its low sensitivity (28-51%) and significant underestimation of peritoneal disease burden 1, 4
• A negative ascitic fluid cytology does not exclude peritoneal carcinomatosis, especially in low-volume disease 1
• Avoid routine PET-CT due to limited utility, particularly in mucinous or diffuse tumors 2, 4
• Do not skip laparoscopy in surgical candidates with T3/T4 tumors or poorly cohesive tumors, as it detects occult disease that changes management 2, 1
• Fine-needle aspiration should be avoided in presumed early-stage disease to prevent cyst rupture and peritoneal seeding 2