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A Proposal for Modification of the PSOGI Classification According to the Ki-67 Proliferation Index in Pseudomyxoma
Álvaro Arjona-Sánchez1,2, Ana Martínez-López3,4, Francisca Valenzuela-Molina5,3
1Unit of Surgical Oncology, Department of Surgery, Reina Sofia University Hospital, Córdoba, Spain. alvaroarjona@hotmail.com.
Background:
Pseudomyxoma peritonei (PMP) is a rare malignancy, classified according to the Peritoneal Surface Oncology Group International (PSOGI) classification, whose response to treatment remains highly heterogeneous within the high-grade (HG) category. Molecular profiling of PMP cases might help to better categorize patients and predict treatment responses.
Methods:
We studied the Ki-67 proliferation rate and P53 overexpression in tissue samples from our historical cohort of HG-PMP patients. We established as cut-off levels the third quartile of each marker to perform univariate and multivariate Cox regression survival analyses. According to these results, the HG-PMP category was divided into subcategories and a new survival analysis was performed.
Results:
A total of 90/117 patients with PMP undergoing cytoreductive surgery (CRS) and hyperthermic intraperitoneal chemotherapy (HIPEC) were selected for secondary analysis. The survival analysis of the HG-PMP category for preoperative variables showed that a proliferation index defined by Ki-67 >15% is a bad prognostic factor, with a hazard ratio (HR) of 3.20 (95% confidence interval [CI] 1.24-8.25). Accordingly, the HG-PMP group was divided using the Ki-67 15% cut-off. The new PSOGI/Ki-67 variable was an independent prognostic factor for overall survival (OS), with an HR of 3.74 (95% CI 1.88-7.47), and disease-free survival (DFS), with an HR of 4.184 (95% CI 1.79-9.75). The estimated 5-year OS rate was 100%, 70% and 24% for the LG-PMP, HG-PMP ≤15% and HG-PMP >15% groups, respectively (p = 0.0001), while the 5-year DFS rate was 90%, 44% and 0%, respectively (p = 0.0001).
Conclusion:
Division of the HG-PMP category of the PSOGI classification, according to the Ki-67 proliferation index, provides two well-defined subcategories, with significant differences in terms of OS and DFS, and hence high prognostic value.
Insights
High-grade pseudomyxoma peritonei (PMP) can be better classified using the Ki-67 proliferation index. This molecular marker improves prognostic accuracy for overall survival and disease-free survival in PMP patients.
Area of Science:
- Oncology
- Molecular Pathology
Background:
- Pseudomyxoma peritonei (PMP) is a rare malignancy with heterogeneous treatment responses within the high-grade (HG) category.
- Current classification systems may not fully capture prognostic variability.
- Molecular profiling offers potential for improved patient stratification.
Purpose of the Study:
- To investigate the prognostic value of Ki-67 proliferation rate in high-grade PMP.
- To refine the Peritoneal Surface Oncology Group International (PSOGI) classification for HG-PMP.
- To identify molecular markers for predicting treatment response and survival outcomes.
Main Methods:
- Retrospective analysis of a historical cohort of 90 HG-PMP patients.
- Ki-67 proliferation index and P53 overexpression assessed in tissue samples.
- Univariate and multivariate Cox regression survival analyses performed using established cut-off levels.
Main Results:
- Ki-67 >15% identified as a significant poor prognostic factor (HR 3.20) for overall survival (OS).
- The HG-PMP category was stratified into HG-PMP ≤15% and HG-PMP >15% based on Ki-67.
- The new PSOGI/Ki-67 classification independently predicted OS (HR 3.74) and disease-free survival (DFS) (HR 4.184).
- Five-year OS rates were 100% (LG-PMP), 70% (HG-PMP ≤15%), and 24% (HG-PMP >15%).
- Five-year DFS rates were 90% (LG-PMP), 44% (HG-PMP ≤15%), and 0% (HG-PMP >15%).
Conclusions:
- Stratifying HG-PMP by Ki-67 proliferation index creates two distinct prognostic subcategories.
- This refined classification significantly improves prediction of OS and DFS.
- Ki-67 serves as a valuable prognostic marker for PMP patients undergoing cytoreductive surgery and HIPEC.
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