Understanding the Peritoneal Cancer Index (PCI) for Ovarian Cancer Patients

The peritoneal cancer index (PCI) is one of the most important tools surgeons use to understand how far ovarian cancer has spread, and to decide the best path forward for treatment. 

If you’ve been diagnosed with advanced ovarian cancer and are facing surgery, there’s a good chance your care team will use this score to guide decisions. But what exactly does it measure? And what does a high or low score actually mean for you?

Here’s what you need to know.

What Is the Peritoneal Cancer Index?

The peritoneal cancer index is a numerical scoring system that quantifies how much cancer is present in the peritoneal cavity: the space in the abdomen that surrounds organs like the intestines, uterus, and bladder. 

It was originally developed in the 1990s for colorectal and gastric cancers, and it has since been applied to ovarian cancer as well.

The abdomen is divided into 13 regions. Each region is scored from 0 to 3 based on the size of the largest tumor implant found there:

• 0: No tumor seen
• 1: Tumor up to 0.5 cm
• 2: Tumor larger than 0.5 cm and up to 5 cm
• 3: Tumor larger than 5 cm

Those scores are added up, giving a total PCI that ranges from 0 to 39. The higher the number, the more widespread the cancer.

Why Does the Peritoneal Cancer Index Matter for Ovarian Cancer?

Ovarian cancer has a tendency to spread along the peritoneal surface (the lining of the abdominal cavity). That pattern of spread is one reason why ovarian cancer staging involves carefully mapping where tumors have traveled.

The PCI helps surgeons answer a critical question before or during surgery: Can we remove all visible disease?

The goal of surgery is to remove as much tumor as possible. This is called debulking surgery, and achieving what surgeons call “complete cytoreduction” — meaning no visible tumor remains — is one of the strongest predictors of survival. And the PCI is one of the strongest predictors of whether that’s achievable. Research in colorectal cancer has shown a near-linear relationship between PCI score and overall survival: each additional point on the scale is associated with worse prognosis. In ovarian cancer, the single most important survival factor is completeness of cytoreduction and PCI helps predict, before or during surgery, how likely that outcome is.

How Is the PCI Score Calculated?

The score is typically calculated during surgery (called intraoperative assessment), once the surgeon can see the full extent of disease inside the abdomen. That said, imaging done before surgery (particularly CT scans) can also be used to estimate the PCI in advance.

Research found that CT-based PCI scores can significantly predict surgical PCI in patients with low-grade serous ovarian cancer (LGSOC), though CT imaging tended to overestimate disease burden in 71% of cases. That’s actually important: it means a high CT-PCI score alone shouldn’t automatically rule a patient out from attempting surgery. (More on this later.)

What Do Different PCI Scores Mean?

There’s no single universally agreed-upon cutoff, and scores should always be interpreted in the full context of a patient’s health and situation. But here’s a general framework:

• PCI 0–10: Limited spread. Strong candidates for complete surgical removal.
• PCI 10–20: Moderate spread. Surgery is still often feasible, though complex.
• PCI 20–30: More extensive spread. Surgery may still be possible, but outcomes vary, and neoadjuvant chemotherapy (chemo before surgery) is often considered for a score greater than 24..
• PCI above 30: Widespread disease. Complete removal becomes significantly harder, and risk of surgical complications rises.

One study found that patients with a PCI of 20 or lower had a 96% chance of achieving complete cytoreduction. For those with a score above 20, that dropped sharply: only 25% achieved complete removal. The study also found that a PCI above 20 was associated with a higher stoma rate and more serious postoperative complications.

PCI and Predicting Whether Surgery Will Work

One of the most valuable uses of the peritoneal cancer index is predicting whether a surgeon will be able to successfully remove all visible disease: a factor that directly affects prognosis.

A research study that followed 167 women with stage III or IV ovarian cancer found the PCI to be an excellent predictor of incomplete cytoreduction, with an area under the curve (AUC) of 0.945: a near-perfect predictive value. Their data suggested that:

• Patients with a PCI below 24 all achieved complete cytoreduction in the study
• Patients with a PCI above 33 had only a 28.6% rate of complete surgery

Based on this, the authors suggested that neoadjuvant chemotherapy — chemotherapy given before surgery to shrink tumors — should be considered when PCI is above 24, especially in patients who may not tolerate a lengthy or complex operation.

Does a High PCI Mean Worse Survival?

This is where the research gets nuanced — and honestly, more hopeful than you might expect.

Research found that patients with high PCI scores had worse overall survival and progression-free survival after primary debulking surgery. The combined hazard ratio for overall survival was 2.79: meaning patients with high PCI had nearly three times the risk of death compared to those with low PCI.

But — and this matters — the single most important predictor of survival wasn’t the PCI itself. It was whether the surgery achieved complete tumor removal. Another study found that suboptimal cytoreduction was the only independent predictive factor for death in multivariate analysis, and not the PCI score on its own.

What this tells us: PCI is a useful tool for predicting surgical outcomes, but it isn’t destiny. A higher score makes complete surgery harder. It doesn’t make it impossible.

PCI and Low-Grade Serous Ovarian Cancer: A Special Case

For patients with LGSOC, the PCI picture is distinct. And this matters a lot.

LGSOC is far less responsive to chemotherapy than high-grade serous ovarian cancer (HGSOC). That means surgery (achieving complete cytoreduction upfront) is arguably more important in LGSOC than in other subtypes. Neoadjuvant chemotherapy, which is often used to shrink tumors before surgery in high-grade cases, may not work as well for LGSOC.

One study specifically looked at PCI in LGSOC patients. They found that CT scans could reasonably estimate how much disease would be found during surgery, but that the score alone didn’t reliably predict whether complete tumor removal was achievable. And crucially, the researchers warned against using imaging results to automatically rule out surgery. In other words: a concerning scan shouldn’t close the door on operating.

That’s critical. It means that even when imaging suggests a higher disease burden, a skilled surgical team may still be able to achieve complete removal in LGSOC patients. Every case deserves individualized evaluation, ideally by a gynecologic oncologist with specific experience in this subtype.

How Is PCI Used Alongside Other Tools?

The PCI doesn’t operate in isolation. Surgeons and oncologists use it alongside other assessments, including:

• CT and MRI imaging to estimate disease burden before surgery
• CA-125 blood tests to monitor tumor markers  
• Laparoscopy: a minimally invasive procedure sometimes used to evaluate the abdomen before committing to full debulking surgery (it’s a procedure where they use a camera to visualize the cancer and sometimes take biopsies)
• The Fagotti score, another laparoscopic scoring tool used to predict whether optimal cytoreduction is achievable

Each tool has its strengths. CT, for example, is better at evaluating tumor burden near major blood vessels and anatomical landmarks. Laparoscopy allows for better visualization of small bowel disease. Together, they give the surgical team the most complete picture possible.

Can PCI Be Assessed Before Surgery?

Yes — and this is an active area of research. Radiologists can calculate a CT-based PCI from preoperative imaging. This matters because it can help the care team decide early whether to proceed with upfront surgery or first try neoadjuvant chemotherapy to reduce the tumor burden.

The catch: CT imaging is not perfectly accurate. It tends to miss very small implants, and as the LGSOC study showed, it can sometimes overestimate disease as well. MRI with diffusion-weighted imaging appears to offer better sensitivity for small deposits, though it isn’t universally used in surgical planning yet.

For most patients, preoperative imaging gives a useful estimate, but the definitive PCI score is still determined in the operating room.

What to Ask Your Surgeon About PCI

If you’re heading into surgery for advanced ovarian cancer, it’s worth asking your surgical team about the peritoneal cancer index. Some questions that may be helpful:

• What does my preoperative imaging suggest about my PCI?
• How does that affect your plan for surgery?
• What is your center’s rate of complete cytoreduction for patients with my level of disease?
• If my PCI turns out to be higher than expected during surgery, what happens next?

Working closely with a gynecologic oncologist who specializes in ovarian cancer (and ideally at a high-volume center) gives you the best chance of achieving complete cytoreduction, regardless of where your PCI lands.

Peritoneal Cancer Index: The Bottom Line

The peritoneal cancer index is a powerful and practical tool for guiding ovarian cancer surgery. A lower score generally means a higher chance of complete tumor removal and a better surgical outcome. A higher score raises the complexity, but it’s not a ceiling.

Research continues to refine how the PCI should be used, especially for subtypes like LGSOC and borderline tumors where the usual rules don’t always apply. 

At Not These Ovaries, we believe that more targeted research into these underserved subtypes is exactly what’s needed. Because decisions like whether to operate, when to operate, and how aggressively to treat should be based on the best available science, not guesswork.