Impact of Previous Abdominal Surgery and Timing of Peritoneal Metastases on Accuracy of Imaging in Predicting the Surgical PCI: A Report From the PRECINCT Study

Background and Aim: In this report from Phase 1 of the prospective, observational, PRECINCT (Pattern of peritoneal dissemination and REsponse to systemic Chemotherapy IN Common and uncommon peritoneal Tumours) study, a correlation was performed between the radiological PCI (peritoneal cancer index; rPCI) and surgical PCI (sPCI). The impact of timing of peritoneal malignancy (PM) and previous abdominal surgery was also studied. Methods: The rPCI and sPCI were considered the ‘same’ if they differed by ≤ 3 points. The agreement was assessed using Bland–Altman analysis and the strength of the agreement was assessed using the concordance correlation coefficient (CCC). The extent of prior surgery was classified according to prior surgical score (PSS). Results: In 707 (79.4%) patients, rPCI and sPCI concurred in 280 (39.6%). In the Bland–Altman analysis, < 40% patients were in the ±3 PCI points limit of acceptable difference. The average difference between the two scores was 4.5 points (95% CI- −5.16 to −3.92). The CCC- was 0.59 for the whole cohort (‘moderate’ concordance) and was not influenced by imaging modality, timing of PM or PSS. Conclusions: The rPCI underestimated sPCI by an average of 4.5 points. The role of peritoneal MRI in patients undergoing iterative procedures and the performance of imaging according to sites of recurrence need further evaluation.