What is the initial treatment approach for a patient diagnosed with peritoneal adenocarcinoma (cancer)?

Initial Treatment Approach for Peritoneal Adenocarcinoma

For patients with peritoneal adenocarcinoma, the initial treatment approach should include systemic chemotherapy for at least 3 months, followed by evaluation for cytoreductive surgery with intraperitoneal chemotherapy in selected patients with low peritoneal cancer index (PCI ≤10) and no extraperitoneal disease. 1

Diagnostic Workup

• Comprehensive imaging:

  • Contrast-enhanced CT scan of thorax, abdomen, and pelvis (mandatory) 1, 2
  • FDG-PET/CT for evaluation of disease extent in single-site/oligometastatic cases 2

• Tissue diagnosis:

  • Biopsy with immunohistochemistry to categorize the carcinoma type 2
  • Diagnostic laparoscopy with peritoneal washings for cytology in potentially resectable disease 1
    • Allows assessment of peritoneal cancer index (PCI) 1
    • Detects radiologically occult metastases 1

• Molecular testing:

  • MSI/MMR testing (universal testing recommended) 1
  • PD-L1 testing for locally advanced or metastatic disease 1
  • CLDN18.2 testing if considering zolbetuximab 1

Initial Treatment Algorithm

1. Systemic chemotherapy (first-line approach):

   • Platinum-based combination chemotherapy for at least 3 months 1, 2
   • Fluoropyrimidine-oxaliplatin regimens show favorable outcomes 3

2. Re-staging after initial chemotherapy 1:

   • CT imaging to assess response
   • Evaluation of PCI score

3. Treatment decision based on response and PCI score:

   a) For patients with low PCI (≤10), stable/improved disease, and no extraperitoneal disease:

   • Multidisciplinary discussion for cytoreduction candidacy 1
   • If complete cytoreduction is likely: Consider gastrectomy with cytoreductive surgery and intraperitoneal chemotherapy (IC/HIPEC) 1
   • If incomplete cytoreduction is predicted: Continue systemic therapy or clinical trial 1

   b) For patients with high PCI (>10), disease progression, or extraperitoneal disease:

   • Continue systemic therapy
   • Consider clinical trial
   • Best supportive care 1

Patient Selection for CRS+HIPEC

HIPEC eligibility criteria:

• Good performance status
• Limited intraperitoneal tumor dissemination (PCI < 20)
• Limited small bowel involvement
• No extra-abdominal metastases 1, 2

Prognostic Considerations

• Poor prognostic factors include:
  • Poor ECOG performance status
  • Male sex
  • Multiple metastatically involved organs
  • Liver metastases
  • Elevated alkaline phosphatase and LDH 2

Important Caveats

1. Positive peritoneal cytology should be considered M1 disease, and surgery as initial treatment is not recommended 1

2. CRS+HIPEC remains controversial in peritoneal carcinomatosis from gastric origin and should be performed only in specialized centers 1, 4

3. Complete cytoreduction is crucial for improved outcomes - the procedure should only be attempted if complete removal of all visible disease is feasible 1

4. Laparoscopic evaluation before definitive surgery helps identify patients who would benefit from optimal cytoreductive surgery 5

5. Peritoneal disease has unique therapeutic responses compared to solid organ metastases and requires specialized management approaches 6

By following this structured approach, patients with peritoneal adenocarcinoma can receive optimal treatment based on their disease characteristics and response to initial therapy.