Reproducibility of the peritoneal regression grading score for assessment of response to therapy in peritoneal metastasis

Aims The four‐tiered peritoneal regression grading score ( PRGS ) assesses the response to chemotherapy in peritoneal metastasis ( PM ). The PRGS is used, for example, to assess the response to pressurised intraperitoneal aerosol chemotherapy ( PIPAC ). However, the reproducibility of the PRGS is currently unknown. We aimed to evaluate the inter‐ and intraobserver variability of the PRGS . Methods and results Thirty‐three patients who underwent at least three PIPAC treatments as part of the PIPAC ‐ OPC 1 or PIPAC ‐ OPC 2 clinical trials at Odense University Hospital, Denmark, were included. Prior to each therapy cycle, peritoneal quadrant biopsies were obtained and three haematoxylin and eosin (H&E)‐stained step sections were scanned and uploaded to a pseudonymised web library. For determining interobserver variability, eight pathologists assessed the PRGS for each quadrant biopsy, and Krippendorff's alpha and intraclass correlation coefficients ( ICC s) were calculated. For determining intraobserver variability, three pathologists repeated their own assessments and Cohen's kappa and ICC s were calculated. A total of 331 peritoneal biopsies were analysed. Interobserver variability for PRGS of each biopsy and for the mean and maximum PRGS per biopsy set was moderate to good/substantial. The intraobserver variability for PRGS of each biopsy and for the mean and maximum PRGS per biopsy set was good to excellent/almost perfect. Conclusions Our data support the PRGS as a reproducible and useful tool to assess response to intraperitoneal chemotherapy in PM. Future studies should evaluate the prognostic and predictive role of the PRGS .