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PubMed This is a summary of 1 peer-reviewed journal articles Updated
Oncology

Subtypes and Staging: The PCI Score and What It Means

At a Glance

Malignant peritoneal mesothelioma (MPM) treatment depends on the cancer cell type (histology) and how widely it has spread in the abdomen, measured by the Peritoneal Cancer Index (PCI). Lower PCI scores often qualify for surgery, while high scores or aggressive subtypes may require immunotherapy.

When you are diagnosed with Malignant Peritoneal Mesothelioma (MPM), your medical team will use two main pieces of information to determine your treatment path: the “flavor” of the cancer cells (histology) and how much cancer is present in the abdomen (staging). Understanding these two factors helps you and your doctors decide if aggressive surgery is the right option for you.

Histological Subtypes: The “Flavor” of the Cancer

The histological subtype refers to what the cancer cells look like under a microscope. According to the Chicago Consensus guidelines, this is the most important factor in predicting how the disease will behave [1].

Subtype Description General Prognosis
Epithelioid The most common type (~75–90% of cases). These cells are more “organized” and tend to grow more slowly [1]. Most Favorable: Many patients live 5 years or longer with proper treatment [1].
Sarcomatoid A highly aggressive type. The cells are shaped like spindles and spread quickly [1]. Most Aggressive: Historically associated with survival of less than 1 year [1]. However, modern immunotherapy is actively changing this landscape and improving outcomes for this subtype [NCT05001880].
Biphasic A mixture of both epithelioid and sarcomatoid cells. Intermediate: The outlook depends heavily on which cell type is more dominant [1].

The Peritoneal Cancer Index (PCI): Mapping the Cancer

To determine the stage or extent of the disease, doctors use a scoring system called the Peritoneal Cancer Index (PCI). This is a way of “mapping” the cancer throughout your abdominal cavity.

The abdomen is divided into 13 specific regions. In each region, the doctor gives a score based on the size of the largest tumor found there:

  • Score 0: No tumor seen.
  • Score 1: Tumor up to 0.5 cm (about the size of a pea).
  • Score 2: Tumor between 0.5 cm and 5 cm.
  • Score 3: Tumor larger than 5 cm or many tumors joined together.

The scores from all 13 regions are added together for a total PCI score. The maximum possible score is 39 [1].

What the PCI Score Means for Treatment

The PCI score is the primary tool used to decide if a patient is a candidate for Cytoreductive Surgery (CRS) and Hyperthermic Intraperitoneal Chemotherapy (HIPEC) [1].

  • Low to Moderate PCI (Often < 20-25): For patients with the epithelioid subtype, a PCI score in this range suggests that a surgeon can likely remove all visible disease [1]. This is called a Complete Cytoreduction (CC-0 or CC-1) and is the primary goal of the procedure.
  • High PCI (Often > 25): When the PCI score is very high, it is much harder to remove all the cancer safely. In these cases, or if the subtype is sarcomatoid, doctors may recommend starting with systemic treatments like immunotherapy instead of going straight to surgery [1].

Diagnostic Laparoscopy

Because CT scans can sometimes under-estimate how much tumor is actually there, your surgical team will often use a diagnostic laparoscopy to calculate your PCI score accurately [1]. This is a minimally invasive, outpatient procedure where a small camera is inserted into the abdomen through a tiny incision. Recovery is typically short, and it provides crucial information before committing to a major open surgery.

Common questions in this guide

What is a PCI score for peritoneal mesothelioma?
The Peritoneal Cancer Index (PCI) is a scoring system used to map the extent of cancer in your abdomen. It divides the abdomen into 13 regions, scoring each area based on tumor size to help doctors determine your best treatment options.
What is the most common subtype of peritoneal mesothelioma?
Epithelioid is the most common histological subtype, accounting for about 75 to 90 percent of cases. These cells are more organized, tend to grow more slowly, and generally have the most favorable prognosis.
What does a high PCI score mean for my treatment?
A high PCI score, typically over 25, means the cancer is more widespread throughout the abdomen. In these cases, it is difficult to safely remove all the cancer with surgery, so doctors often recommend systemic treatments like immunotherapy instead.
How do doctors calculate my exact PCI score?
While CT scans provide a baseline, doctors often perform a diagnostic laparoscopy to get a highly accurate PCI score. This is a minimally invasive outpatient procedure where a surgeon uses a small camera to look directly inside your abdomen.
Can I have CRS and HIPEC surgery if my mesothelioma is sarcomatoid?
Because sarcomatoid mesothelioma is a highly aggressive subtype that spreads quickly, immediate surgery is usually not recommended. Instead, patients with this subtype are increasingly treated with modern systemic immunotherapy to improve outcomes.

Questions to Ask Your Doctor

Curated prompts to bring to your next appointment.

  1. 1.What is my specific histological subtype, and what percentage of it is epithelioid versus sarcomatoid?
  2. 2.What is my estimated Peritoneal Cancer Index (PCI) score based on my imaging or laparoscopy?
  3. 3.Based on my PCI score and histology, do you believe we can achieve a Complete Cytoreduction (CC-0 or CC-1)?
  4. 4.If my PCI score is high or my subtype is aggressive, what are my options for systemic immunotherapy?

Questions For You

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References

References (1)
  1. 1

    Molecular alterations and potential actionable mutations in peritoneal mesothelioma: a scoping review of high-throughput sequencing studies.

    Dietz MV, van Kooten JP, Paats MS, et al.

    ESMO open 2023; (8(4)):101600 doi:10.1016/j.esmoop.2023.101600.

    PMID: 37453150

This page provides educational information about malignant peritoneal mesothelioma staging and PCI scores. Always consult your surgical oncologist to interpret your specific pathology reports and determine your treatment eligibility.

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