What is the recommended staging and treatment approach for a newly diagnosed adult female patient with primary peritoneal cancer and no significant past medical history, using Peritoneal Cancer Index (PCI) staging?

PCI Staging for Primary Peritoneal Tumor

Staging System

Primary peritoneal cancer is staged using the FIGO staging system for epithelial ovarian cancer, where primary peritoneal cancer is classified as Stage II disease ("tumour involves one or both ovaries or fallopian tubes with pelvic extension or primary peritoneal cancer"), and the Peritoneal Cancer Index (PCI) is used to quantify disease burden for surgical planning. 1

FIGO Staging Classification

Primary peritoneal cancer falls within the FIGO staging framework as follows: 1

• Stage II: Tumor involves pelvic extension or primary peritoneal cancer

  • Stage IIA: Extension to uterus, fallopian tubes, and/or ovaries
  • Stage IIB: Extension to other pelvic intraperitoneal tissues

• Stage III: Cytologically or histologically confirmed spread to peritoneum outside pelvis and/or retroperitoneal lymph nodes

  • Stage IIIA1: Positive retroperitoneal lymph nodes only
  • Stage IIIA2: Microscopic extra-pelvic peritoneal involvement
  • Stage IIIB: Macroscopic peritoneal metastasis ≤2 cm
  • Stage IIIC: Macroscopic peritoneal metastasis >2 cm

• Stage IV: Distant metastasis excluding peritoneal metastases

  • Stage IVA: Pleural effusion with positive cytology
  • Stage IVB: Parenchymal metastases and extra-abdominal organ involvement

Peritoneal Cancer Index (PCI) Scoring

PCI Calculation Method

The PCI quantifies peritoneal disease burden by dividing the abdomen into 13 regions, with each region scored 0-3 based on lesion size: 2, 3

• 0: No visible tumor
• 1: Tumor up to 0.5 cm
• 2: Tumor 0.5-5 cm
• 3: Tumor >5 cm or confluence

Total PCI score ranges from 0-39, with PCI ≥20 traditionally indicating extensive disease burden. 2, 4

Clinical Significance of PCI Thresholds

• PCI <20: Predicts optimal cytoreduction with 83-85% accuracy and is the best predictor of successful complete cytoreductive surgery 4
• PCI ≥20: Associated with higher likelihood of suboptimal cytoreduction, though 46% of patients may still achieve adequate cytoreduction 2
• PCI ≤10: Indicates limited disease burden suitable for cytoreductive surgery plus HIPEC in selected malignancies 5

Important Caveats About PCI Assessment

The PCI score increases by approximately 2 points between initial assessment and completion of cytoreductive surgery, reflecting more accurate disease quantification after surgical exploration. 3 This means preoperative imaging-based PCI systematically underestimates true disease burden.

Concordance between radiologic and surgical PCI is moderate (correlation 0.59-0.65), with sensitivity of 76% and specificity of 69% for detecting PCI ≥20. 2 CT imaging has poor sensitivity (28-51%) for detecting peritoneal metastases, while diagnostic laparoscopy achieves 85% sensitivity and 100% specificity. 1

Treatment Approach Based on PCI

For Primary Peritoneal Cancer (Ovary-Like Presentation)

Women with primary peritoneal cancer should be treated identically to FIGO Stage III ovarian cancer: optimal surgical debulking (cytoreductive surgery) followed by platinum-based combination chemotherapy (carboplatin plus paclitaxel). 1

Surgical Management Algorithm

1. Evaluation by gynecologic oncologist prior to treatment initiation 1

2. Staging workup: 1

   • Midline laparotomy with inspection and palpation of entire abdominal cavity
   • Peritoneal washings for cytology
   • Assessment of all 13 peritoneal regions for PCI calculation
   • Lymph node evaluation (retroperitoneal)

3. Cytoreductive surgery goals: 1

   • Complete macroscopic tumor removal (CC-0 or CC-1 residual disease)
   • Peritonectomy procedures as needed
   • Lymphadenectomy if nodes suspicious

4. Adjuvant chemotherapy: 6

   • Platinum-based combination (carboplatin/paclitaxel) mandatory for advanced stage
   • Initiate within 6-8 weeks post-operatively to avoid compromising outcomes

Role of HIPEC in Primary Peritoneal Cancer

For primary peritoneal cancer with isolated peritoneal carcinomatosis, assessment for cytoreductive surgery with peritonectomy may be considered at experienced referral centers, but HIPEC is NOT recommended as there are no data supporting its use in this setting. 1

Critical selection criteria for cytoreductive surgery consideration: 1

• Good performance status (ECOG 0-2)
• Low peritoneal disease burden (PCI ≤10-20)
• No extraperitoneal metastases
• Treatment at specialized high-volume center
• Anticipated complete cytoreduction feasible

Contraindications to Cytoreductive Surgery

Patients should receive systemic chemotherapy alone (not surgery) if: 1, 5

• ECOG performance status ≥3 or Karnofsky <60%
• High PCI (>20 for most tumors, >10 for gastric-type)
• Extensive small bowel involvement
• Extraperitoneal metastases present
• Incomplete cytoreduction anticipated

Diagnostic Workup Algorithm

Initial Assessment

1. CT abdomen/pelvis with IV and oral contrast plus chest imaging (CT preferred) 1

2. Tissue diagnosis with immunohistochemistry: 1

   • Estrogen and progesterone receptors (to confirm gynecologic origin)
   • CK7/CK20 pattern
   • PAX8, WT-1 (ovarian markers)
   • CA-125 level

3. Consider diagnostic laparoscopy if imaging equivocal or to confirm resectability, given superior sensitivity (85%) versus CT (28-51%) 1

4. PET-CT or diffusion-weighted MRI may refine assessment but PET-CT detects only 3% of occult peritoneal metastases 1, 5

Predictors of Suboptimal Cytoreduction

Clinical factors indicating likely suboptimal surgery: 1

• Age ≥60 years
• CA-125 ≥500 U/mL
• ASA Physical Status 3-4

Radiologic findings predicting suboptimal cytoreduction: 1

• Retroperitoneal lymph nodes above renal hilum >1 cm
• Diffuse small bowel adhesions or thickening
• Small bowel mesentery lesions >1 cm
• Superior mesenteric artery root lesions >1 cm
• Perisplenic lesions >1 cm
• Lesser sac lesions >1 cm

Common Pitfalls to Avoid

• Do not rely solely on CT imaging to determine resectability, as it significantly underestimates peritoneal disease burden 1, 2
• Do not use PCI ≥20 as absolute contraindication to surgery, as nearly half of these patients may still achieve adequate cytoreduction 2
• Do not add HIPEC to cytoreductive surgery for primary peritoneal cancer outside clinical trials, as evidence is lacking 1
• Do not delay adjuvant chemotherapy beyond 6-8 weeks post-operatively 6
• Do not attempt cytoreductive surgery at low-volume centers without substantial experience in peritoneal surface malignancies 1, 5