Prediction of non-resectability in tubo-ovarian cancer patients using Peritoneal Cancer Index – A prospective multicentric study using imaging (ISAAC study)

Background: The aim was to evaluate the performance of the Peritoneal Cancer Index (PCI) using imaging (ultrasound, contrast-enhanced computed tomography (CT), and whole-body diffusion-weighted magnetic resonance imaging (WB-DWI/MRI) in assessing peritoneal carcinomatosis and predicting non-resectability in tubo-ovarian carcinoma patients. Methods: This was a prospective multicenter observational study. We considered all patients with suspected primary ovarian/tubal/peritoneal cancer who underwent preoperative ultrasound, CT, and WB-DWI/MRI (if available). The optimal cut off value for assessing the performance of the methods in predicting non-resectability was identified at the point at which the sensitivity and specificity were most similar. The reference standard to predict non-resectability was surgical outcome in terms of residual disease >1 cm or surgery not feasible. Agreement between imaging methods and surgical exploration in assessing sites included in the PCI score was evaluated using the Intraclass Correlation Coefficient (ICC). Results: 242 patients were included from January 2020 until November 2022. The optimal PCI cut-off for predicting non-resectability for surgical exploration was >12, which achieved the best AUC of 0.87, followed by ultrasound with a cut-off of >10 and AUC of 0.81, WB-DWI/MRI with a cut-off of >12 and AUC of 0.81, and CT with a cut-off of >11 and AUC of 0.74. Using ICC, ultrasound had very high agreement (0.94) with surgical PCI, while CT and WB-DWI/MRI had high agreement (0.86 and 0.87, respectively). Conclusion: Ultrasound performed by an expert operator had the best agreement with surgical findings compared to WB-DWI/MRI and CT in assessing radiological PCI. In predicting non-resectability, ultrasound was non-inferior to CT, while its non-inferiority to WB-DWI/MRI was not demonstrated.