Prognostic value of Combined Progression Index (CPI) in 132 patients with unresectable peritoneal metastasis treated with Pressurized IntraPeritoneal Aerosol Chemotherapy.

Pressurized IntraPeritoneal Aerosol Chemotherapy (PIPAC) is a palliative treatment for patients with unresectable peritoneal metastasis (PM) from gastrointestinal and gynecological cancers. Few prognostic markers for stratification of patients with PM receiving PIPAC directed treatments exist. The Combined Progression Index (CPI) has been proposed as a prognostic tool in these patients. CPI combines overall change in the histological Peritoneal Regression Grading Score (PRGS) from peritoneal quadrant biopsies taken prior to PIPAC treatments 1 and 3 and peritoneal fluid (PF) cytology at PIPAC 3. Our aim was to investigate the prognostic value of CPI in unresectable PM patients treated with PIPAC. We performed a retrospective study of prospectively collected data based on all PM patients treated with PIPAC at Odense PIPAC Center from 2015 to 2024. Positive CPI was defined as an increase in PRGS from peritoneal quadrant biopsies taken prior to PIPAC 1 and PIPAC 3 and/or positive PF cytology at PIPAC 3. Positive PF cytology was defined as malignant cells or cells suspicious of malignancy. Survival data were analyzed using Kaplan-Meier graphs, log-rank test, and univariable and multivariable Cox proportional hazards regression. Inclusion criteria were fulfilled by 132 patients. In the entire cohort and PM from gastric cancer (GC-PM), but not in PM from colon or pancreatic cancer, CPI-positivity was associated with shorter OS (P < 0.01). In both GC-PM and the entire cohort, CPI-positivity had independent negative prognostic value (P = 0.005). In conclusion, our data indicate that CPI holds clinically relevant prognostic information. As it in some PIPAC-treated patients is only possible to perform either cytology or PRGS, we recommend using both methods whenever feasible, as this also enables assessment of CPI.