The peritoneal cancer index (PCI) is not itself a disease, but rather a specialized scoring tool that helps doctors measure how much cancer has spread across the membrane lining the abdomen, known as the peritoneum. This numerical score plays a vital role in planning treatment and predicting outcomes for patients whose cancer has reached this delicate inner lining.

Understanding the Role of PCI in Cancer Treatment Planning

When cancer spreads to the peritoneum—the thin membrane that lines the abdominal cavity and covers organs inside it—doctors need a reliable way to understand the extent of that spread. This is where the peritoneal cancer index becomes essential. Developed by French surgeon Paul H. Sugarbaker in the 1980s, the PCI provides a standardized method for doctors to communicate about how much cancer is present and where exactly it has settled in the abdomen.^[2]

The index works by dividing the abdomen into 13 specific regions and assigning each region a score based on tumor size. The scores range from 0 (no visible tumor) to 3 (tumors larger than 5 centimeters or widespread disease in that area). When all regions are added together, the total PCI score can range from 0 to 39. A higher number indicates more extensive cancer spread throughout the peritoneum.^[2][3]

This scoring system serves multiple crucial purposes in cancer care. First, it helps doctors determine whether surgery to remove visible tumors—called cytoreductive surgery (a procedure aimed at reducing the amount of cancer in the body)—is likely to be successful. Second, it assists in predicting how well a patient might respond to treatment. Third, it provides a common language that surgeons, oncologists, and radiologists can use when discussing a patient’s case, ensuring everyone understands the severity and distribution of the disease.^[2][4]

The PCI is most commonly used in patients with peritoneal cancer that originated from other organs. The cancers that most frequently spread to the peritoneum include ovarian cancer, colorectal cancer, stomach cancer, pancreatic cancer, and appendiceal cancer. It’s also used for a rare condition called pseudomyxoma peritonei, which produces jelly-like mucus in the abdomen.^[2][5][10]

How PCI is Measured and Assessed

Calculating the peritoneal cancer index requires a detailed examination of the abdominal cavity. This assessment can be done in different ways, each with its own advantages. The most accurate method involves direct visualization during surgery, either through minimally invasive surgery using a camera (laparoscopy) or during open surgery. When surgeons can actually see inside the abdomen, they can precisely measure tumor sizes and assign scores to each of the 13 regions.^[2]

However, doctors increasingly rely on advanced imaging techniques to estimate the PCI before surgery. Computed tomography (CT scans, which use X-rays and computer processing to create detailed cross-sectional images) is the most commonly used method because of its availability and relatively high accuracy. CT scans can identify tumor implants, fluid buildup in the abdomen (called ascites, an accumulation of fluid in the peritoneal cavity), and changes in the fatty tissue that lines organs.^[12]

Magnetic resonance imaging (MRI, which uses powerful magnets and radio waves to create detailed images) can also be used to assess the peritoneum. MRI is particularly good at detecting implants larger than 10 millimeters, and its sensitivity is comparable to CT for these larger tumors. Some studies suggest that PET/CT (a combination scan that shows both structure and metabolic activity) may be even more sensitive, though its practical usefulness for routine PCI assessment remains under discussion.^[12]

It’s important to understand that imaging has limitations. Smaller tumor deposits, especially those under 5 millimeters, can be difficult or impossible to see on scans. This means that the PCI calculated from imaging before surgery may underestimate the true extent of disease. A negative or low-score scan doesn’t necessarily rule out peritoneal cancer, which is why direct surgical inspection often provides the most accurate assessment.^[11][12]

Standard Treatment Approaches Guided by PCI

The peritoneal cancer index plays a fundamental role in determining which treatments are appropriate for each patient. When cancer has spread to the peritoneum, the standard treatment approach typically combines surgery with specialized chemotherapy delivered directly into the abdominal cavity.

The primary surgical treatment is cytoreductive surgery, also known as CRS. The goal is complete removal of all visible tumor tissue from the peritoneum and affected organs. This can be extensive surgery, sometimes involving removal of parts of the peritoneum, portions of the bowel, the spleen, the gallbladder, or other structures where cancer has spread. The success of this surgery is measured by the completeness of cytoreduction (CC) score, which indicates how much tumor remains after surgery. A CC-0 or CC-1 score means complete or nearly complete removal, which is associated with better survival.^[2][5][10]

The PCI score helps surgeons predict whether complete cytoreductive surgery is achievable. Generally, lower PCI scores suggest a higher likelihood of successful complete tumor removal. Different cancers have different PCI thresholds for surgical candidacy. For example, in ovarian cancer, a PCI score above 13 or above 24 has been associated with worse survival outcomes and lower chances of complete tumor removal. For pseudomyxoma peritonei, optimal cutoff points differ between low-grade and high-grade disease: around PCI 21 for low-grade and PCI 25 for high-grade disease.^[4][3][10]

Following cytoreductive surgery, many patients receive hyperthermic intraperitoneal chemotherapy, abbreviated as HIPEC. This treatment involves washing the abdominal cavity with heated chemotherapy solution during surgery, immediately after tumor removal. The heat helps the chemotherapy penetrate tissue more effectively and may kill cancer cells that remain after surgery but are too small to see. The chemotherapy drugs are heated to temperatures between 41 and 43 degrees Celsius (about 106 to 109 degrees Fahrenheit) and circulated throughout the abdomen for 30 to 90 minutes.^[2][5][8]

The combination of cytoreductive surgery and HIPEC has significantly improved outcomes for patients with peritoneal cancer. This approach can extend survival and, in some cases, offer the possibility of long-term disease control. However, it’s major surgery with significant risks, including infection, bleeding, intestinal injury, blood clots, and complications from chemotherapy. Recovery typically takes several weeks to months.^[2][5]

Not all patients are candidates for this combined approach. Very high PCI scores often indicate that complete tumor removal is not possible. In ovarian cancer, for instance, only about 28.6% of patients with PCI higher than 33 achieved complete cytoreduction in one study. In these situations, doctors may recommend alternative treatments such as standard systemic chemotherapy (drugs given through the bloodstream) or other palliative approaches focused on symptom management and quality of life.^[9]

For patients with high PCI scores or cancer that cannot be completely removed surgically, another option is pressurized intraperitoneal aerosolized chemotherapy, known as PIPAC. This is a newer technique where chemotherapy is delivered as a pressurized aerosol (a fine mist) directly into the abdominal cavity during minimally invasive surgery. PIPAC can be repeated multiple times and is being explored for patients whose disease is too extensive for cytoreductive surgery.^[2]

Research and Innovative Approaches in PCI-Guided Treatment

Ongoing research is exploring how to better predict PCI scores before surgery and how to use this information to improve treatment selection and outcomes. Scientists are investigating whether blood tests, artificial intelligence analysis of imaging, or combinations of different markers can provide more accurate estimates of peritoneal tumor burden without requiring surgery.

One area of investigation involves the concept of “selected PCI.” Instead of scoring all 13 abdominal regions, some researchers have found that focusing on specific high-impact areas may be just as predictive but simpler to assess. These critical regions include the hepatic hilum (the area where blood vessels enter the liver, corresponding to region 2) and the small intestine regions (regions 9 through 12). Tumors in these areas are technically challenging to remove and strongly influence whether complete cytoreduction is possible.^[3][10]

In pseudomyxoma peritonei studies, both total PCI and selected PCI (regions 2 plus 9-12) showed excellent ability to predict surgical success, with very similar accuracy. However, the selected PCI is simpler and faster to calculate, which could be advantageous in clinical practice. For low-grade pseudomyxoma peritonei, a selected PCI cutoff of 5 and total PCI cutoff of 21 were identified as optimal for predicting complete resection. For high-grade disease, these cutoffs were 8 for selected PCI and 25 for total PCI.^[3][10]

Researchers are also developing better imaging techniques to visualize peritoneal disease. New MRI protocols, enhanced CT scanning methods, and artificial intelligence algorithms that can analyze images to detect small tumor deposits are all under investigation. The goal is to provide surgeons with the most accurate possible roadmap before they enter the operating room, helping them plan procedures more effectively and counsel patients more accurately about their likelihood of successful treatment.^[3]

Another research direction involves combining the PCI with other prognostic markers. For example, in gastric cancer with peritoneal metastasis, scientists have explored combining PCI with blood-based inflammatory markers (such as neutrophil-to-lymphocyte ratio and platelet-to-lymphocyte ratio) to create composite scores that might better predict outcomes. These integrated scoring systems could help doctors make more personalized treatment decisions.^[1]

Clinical trials are examining whether treatment strategies can be tailored based on PCI scores. Some studies are investigating whether patients with moderately high PCI scores might benefit from chemotherapy before surgery to shrink tumors and make complete cytoreduction more achievable. Others are testing whether different chemotherapy regimens during HIPEC might work better for different PCI ranges. These investigations are taking place in cancer centers in Europe, the United States, Asia, and other regions around the world.^[1][4]

Most common treatment methods

• Cytoreductive surgery (CRS)
  • Surgical removal of all visible tumor tissue from the peritoneum and affected organs
  • May involve removal of parts of the peritoneum, bowel segments, spleen, gallbladder, or other structures
  • Success measured by completeness of cytoreduction (CC) score
  • PCI score helps predict likelihood of achieving complete tumor removal
  • Lower PCI scores generally associated with better surgical outcomes
• Hyperthermic intraperitoneal chemotherapy (HIPEC)
  • Heated chemotherapy solution circulated in abdominal cavity during surgery
  • Performed immediately after cytoreductive surgery
  • Chemotherapy heated to 41-43 degrees Celsius for 30-90 minutes
  • Heat helps chemotherapy penetrate tissue more effectively
  • Combined with cytoreductive surgery, has significantly improved survival outcomes
• Pressurized intraperitoneal aerosolized chemotherapy (PIPAC)
  • Chemotherapy delivered as pressurized aerosol mist into abdominal cavity
  • Performed during minimally invasive surgery
  • Can be repeated multiple times
  • Option for patients with high PCI scores or unresectable disease
  • Being explored for patients whose disease is too extensive for cytoreductive surgery
• Systemic chemotherapy
  • Chemotherapy drugs delivered through the bloodstream
  • May be used when PCI scores indicate surgery is unlikely to be successful
  • Can be given before surgery to shrink tumors in some cases
  • Standard option for patients who are not candidates for cytoreductive surgery
• Imaging and staging procedures
  • CT scans (computed tomography) most commonly used to estimate PCI before surgery
  • MRI (magnetic resonance imaging) can detect tumor implants larger than 10 millimeters
  • PET/CT may provide additional information about metabolic activity
  • Staging laparoscopy provides most accurate PCI assessment through direct visualization
  • Advanced imaging helps plan treatment and predict surgical outcomes