Solass W, et al. - Given that the 4-tiered Peritoneal Regression Grading Score (PRGS) is assessing response to chemotherapy in peritoneal metastasis (PM), researchers assessed the interobserver and intraobserver variability of the PRGS. Study participants included 33 patients who had at least 3 Pressurized IntraPeritoneal Aerosol Chemotherapy (PIPAC) treatments as part of the PIPAC-OPC1 or PIPAC-OPC2 clinical trials at Odense University Hospital, Denmark. Among 331 peritoneal biopsies analyzed, the interobserver variability of each biopsy for PRGS and the mean and maximum PRGS for each biopsy set was moderate to good/substantial. The intraobserver variability of each biopsy for PRGS and the mean and maximum PRGS for each biopsy set was good to excellent. According to findings, PRGS as a reproducible and useful tool for evaluating intraperitoneal chemotherapy responses in PM was supported.