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The Peritoneal Regression Grading Score (PRGS) is a scoring system used to assess the response of patients with pseudomyxoma peritonei (PMP) to treatment. It is a four-tiered scoring system, with scores ranging from 1 to 4.  A score of 1 means there is no visible residual disease, while a score of 4 means there is significant residual disease. The PRGS helps doctors to determine the effectiveness of treatment and to make decisions about further treatment options.

In the context of the peritoneal regression grading (PRG) score for pseudomyxoma peritonei, regression refers to the shrinkage, reduction in size, or disappearance of the peritoneal tumour components in response to treatment. It may consist of:

  • lessening of the mucinous ascites (abdominal fluid)
  • peritoneal lumps and nodules shrinking or getting smaller
  • Visible peritoneal tumour implants disappearing

What are the four tiers of PRGS?

The four PRGS tiers are:

  • Grade 1:
    Complete resonse with no macroscopic disease remaining. This ideal response offers the best chance for long-term disease-free survival
  • Grade 2:
    Major, regression features, few residual tumour cells
  • Grade 3:
    Minor, some regressive features but predominance of residual tumour cells
  • Grade 4
    no response (tumour cells without any regressive features). Poorer response with worse prognosis. Additional surgeries and/or clinical trials may be options to try and improve outcomes

Key points about the PRGS

The Peritoneal Regression Grading Score provides an objective measure of how much residual disease is left after cytoreductive surgery and HIPEC (CRS/HIPEC). Larger amounts indicate a poorer treatment response and worse prognosis. Grades 1 and 2 responses are associated with significantly longer progression-free and overall survival. High-grade responses (3-4) lead to earlier recurrence. The PRGS helps guide postoperative management and monitoring plans. Closer follow up is needed for higher grades to quickly detect any recurrence. More aggressive treatment may also be recommended. The PRGS allows for comparison of results across different centres and surgeons. A centre’s average PRGS scores may represent their skill and ability to maximize cytoreduction for the best outcomes. Grade 1-2 PRGSs tend to correlate with experienced high-volume teams. Ongoing research aims to expand the PRGS to incorporate additional factors like tumour biology, patient health, and chemotherapy details. But smaller deposits of residual disease remain the strongest prognostic indicator. PRGS results, along with other factors visible in a laboratory, help determine if patients are candidates for adjuvant HIPEC, which can improve outcomes when given after an optimal primary procedure. Educational efforts promote raising minimally acceptable PRGS standards to continue advancing this complex and specialized treatment. The goal is achieving Grade 1-2 responses for more and more patients.


Peritoneal regression grading score (PRGS) in peritoneal metastasis...

Solass W, Meisner C, Kurtz F, Nadiradze G, Reymond MA, Bösmüller H. Peritoneal regression grading score (PRGS) in peritoneal metastasis: How many biopsies should be examined? Pleura and Peritoneum. 2022;7(4):179-185. doi:10.1515/pp-2022-0118

Importance of biopsy site selection for peritoneal regression grading score (PRGS)...

Fallah M, Detlefsen S, Ainsworth AP, et al. Importance of biopsy site selection for peritoneal regression grading score (PRGS) in peritoneal metastasis treated with repeated pressurized intraperitoneal aerosol chemotherapy (PIPAC). Pleura and Peritoneum. 2022;7(3):143-148. doi:10.1515/pp-2022-0108

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