What is the treatment approach for a patient with peritoneal carcinomatosis?

Treatment of Peritoneal Carcinomatosis

The treatment approach for peritoneal carcinomatosis depends critically on the primary tumor origin, with colorectal cancer requiring complete cytoreductive surgery (CRS) WITHOUT hyperthermic intraperitoneal chemotherapy (HIPEC), while gastric cancer may benefit from CRS plus HIPEC in highly selected patients with limited disease burden (PCI ≤10). 1, 2

Primary Tumor Identification is Essential

The first critical step is determining the primary cancer source, as this fundamentally alters treatment strategy:

• Women with serous adenocarcinoma should be treated as FIGO III ovarian cancer with optimal cytoreductive surgery followed by platinum-based chemotherapy 3
• Colorectal origin requires complete CRS without HIPEC based on the PRODIGE 7 trial, which demonstrated no survival benefit and increased late complications with HIPEC addition 1, 2
• Gastric cancer origin may warrant CRS plus HIPEC in highly selected patients at specialized centers 1

Diagnostic Workup Required

• For women: Immunostaining for estrogen/progesterone receptors and mammogram to exclude breast cancer 3
• For men: PSA, alpha-fetoprotein, and beta-HCG to exclude extragonadal germ cell tumors and prostate cancer 3
• All patients: Complete histopathological evaluation with immunohistochemistry, CT chest/abdomen/pelvis 3
• Note: Diagnostic laparoscopy has 85% sensitivity and 100% specificity for detecting peritoneal metastases, while CT imaging has only 28-51% sensitivity 1

Colorectal Cancer Peritoneal Carcinomatosis

Patient Selection Algorithm

Proceed with CRS evaluation if:

• PCI < 20 4, 2
• No extraperitoneal metastases 4, 2
• Good performance status (ECOG 0-2) 1
• Limited small bowel disease 4
• Complete cytoreduction appears achievable 2

Critical Evidence: The ASCO 2023 guideline reports CRS reduces death risk with hazard ratio 0.55 (95% CI, 0.32-0.95), translating to 181 fewer deaths per 1,000 patients at 24 months compared to systemic chemotherapy alone 2

Treatment Protocol

For eligible patients (PCI < 20, no extraperitoneal disease):

• Complete cytoreductive surgery WITHOUT HIPEC 1, 2
• Treatment must be performed at specialized centers with substantial CRS experience 1
• 15% of patients remain progression-free at 5 years with complete CRS 1
• Mortality rate related to CRS is 8% 1

For ineligible patients (PCI ≥ 20 or extraperitoneal metastases):

• Systemic chemotherapy with fluoropyrimidines combined with oxaliplatin or irinotecan 2
• Add anti-EGFR therapy for left-sided RAS wild-type tumors 2
• Add anti-VEGF therapy based on tumor lateralization and RAS mutation status 2

Gastric Cancer Peritoneal Carcinomatosis

Patient Selection Algorithm

ECOG Performance Status Assessment First:

• ECOG PS 0-2: Proceed to disease burden assessment 1
• ECOG PS ≥3 or Karnofsky <60%: Offer best supportive care only 1

Disease Burden Assessment (Peritoneal Cancer Index):

• Low PCI (≤10): Candidate for systemic therapy followed by potential CRS + HIPEC 1
• High PCI (>10): Systemic therapy, clinical trial, or best supportive care only 1

Treatment Protocol

For highly selected patients (PCI ≤10, ECOG 0-2):

• Initial systemic therapy with molecular testing (HER2, PD-L1, CLDN18.2, MSI/MMR) 1
• Treatment based on molecular profile 1
• CRS + HIPEC at specialized centers if complete resection achievable 1
• Median overall survival with CRS + HIPEC: 11-24 months vs. 5-6 months with systemic chemotherapy alone 1

Standard treatment remains systemic chemotherapy as recommended by most international guidelines, though peritoneal-directed strategies are emerging 4

Peritoneal Carcinomatosis from Unknown Primary

Treatment Algorithm

For women with serous adenocarcinoma:

• Optimal cytoreductive surgery (debulking) as first step 3
• Platinum-based chemotherapy following surgery 3
• Treat as FIGO III ovarian cancer 3

For poorly differentiated carcinoma:

• Platinum-based combination chemotherapy as first-line treatment 3
• Reevaluate after 2-3 cycles with individualized tests 3

For refractory disease with specific markers:

• Immunotherapy with checkpoint inhibitors if TMB-H ≥10 mut/Mb or MSI-H/dMMR 3
• Consider if high PD-L1 expression present 3

Critical Pitfalls to Avoid

Do NOT add HIPEC to CRS for colorectal cancer: The PRODIGE 7 trial definitively showed no survival benefit (HR 1.00,95% CI 0.63-1.58) and increased toxicity 1, 2

Do NOT attempt CRS in patients with:

• PCI ≥ 20 for colorectal cancer 2
• PCI > 10 for gastric cancer 1
• Extensive small bowel involvement 4
• Poor performance status 1
• Extraperitoneal metastases 4, 2

Do NOT rely on CT imaging alone: CT has only 28-51% sensitivity for detecting peritoneal metastases; diagnostic laparoscopy is superior with 85% sensitivity 1

Multidisciplinary Team Requirements

Treatment decisions require a multidisciplinary team including:

• Medical oncology expertise 1
• Surgical oncology with substantial CRS experience 1
• Radiology 1
• Pathology 1
• Palliative care specialists 1

Functional status is the most important prognostic factor during treatment 3