Peritoneal Cancer Index (PCI): what it is and how it is used

The PCI is a tool used in surgical oncology to quantify the extent of peritoneal carcinomatosis. It is calculated by dividing the abdomen into 13 regions and giving each one a score from 0 to 3 according to the size of the tumor implants. The total can reach 39 points and reflects the overall tumor burden.

The abdomen is divided into 13 regions (9 abdominopelvic regions and 4 segments of the small bowel). Each region is scored from 0 to 3: 0 with no visible lesions, 1 if the nodules are smaller than 0.5 cm, 2 if the lesions measure between 0.5 and 5 cm, and 3 if the implants are larger than 5 cm or confluent. The sum of all the scores gives the total PCI.

A high PCI indicates extensive involvement of the peritoneum by tumor implants and is associated with a greater tumor burden and a worse prognosis in general. A high PCI can also make complete cytoreductive surgery technically unfeasible or of insufficient clinical benefit.

The PCI is one of the most important factors in deciding on cytoreductive surgery, but not the only one. The final decision also depends on the type of primary tumor, the patient's general condition, the response to previous treatments and the possibility of achieving complete cytoreduction (CC-0).

The most reliable PCI is obtained during exploratory surgery, which allows every region to be inspected directly. Imaging tests (CT, MRI, PET-CT) can estimate a radiological PCI, but they tend to underestimate the disease because many small implants are not detected. Diagnostic laparoscopy is a minimally invasive alternative that is more accurate than imaging.

The PCI is calculated at the start of surgery and measures the extent of the disease before resection. The CC Score (Completeness of Cytoreduction) is calculated at the end of the operation and assesses how complete the resection was: CC-0 with no visible residual disease, CC-1 residual disease smaller than 2.5 mm, CC-2 between 2.5 mm and 2.5 cm, and CC-3 larger than 2.5 cm. A low PCI combined with CC-0 is associated with the best oncological outcomes.

The abdomen is divided into 13 regions: central (1), right upper quadrant (2), epigastrium (3), left upper quadrant (4), left flank (5), left lower quadrant (6), pelvis (7), right lower quadrant (8) and right flank (9), plus four segments of the small bowel: proximal jejunum (10), distal jejunum (11), proximal ileum (12) and distal ileum (13).

The PCI is used in most peritoneal carcinomatoses: pseudomyxoma peritonei, peritoneal mesothelioma, and colorectal, gastric, ovarian and appendiceal cancer. Interpretation and decision thresholds vary with the primary tumor: higher PCI values are accepted in pseudomyxoma and mesothelioma, while lower values are preferred in gastric or colorectal cancer before indicating cytoreduction.

The PCI should be calculated by a surgeon with specific experience in peritoneal carcinomatosis, usually within a unit specialized in cytoreduction and HIPEC. Correctly identifying small implants, assessing all 13 regions systematically and making the final decision on surgical feasibility require specific training and a high volume of cases.

When the PCI exceeds the thresholds accepted for each type of tumor, radical surgery may not be indicated. In those cases alternatives are considered, such as PIPAC (pressurized intraperitoneal aerosol chemotherapy), systemic treatment or inclusion in clinical trials. The decision is always made by a multidisciplinary committee, taking into account the patient's condition and the aims of treatment.

Yes, in some cases neoadjuvant systemic chemotherapy can reduce the peritoneal tumor burden and, with it, the PCI. This can turn patients who were initially not candidates into candidates for cytoreductive surgery. The response depends on the type of tumor, its chemosensitivity and the biology of each case, so the assessment should be made at a center with specific experience.