OC04.01: Prediction of non‐resectability in ovarian cancer patients using peritoneal cancer index: a prospective multicentre study using imaging (ISAAC study)

To evaluate the performance of the peritoneal cancer index (PCI) using imaging (ultrasound, computed tomography (CT), and whole-body diffusion-weighted magnetic resonance imaging (WB-DWI/MRI) in assessing the peritoneal carcinomatosis and predicting non-resectability in advanced tubo-ovarian cancer patients. This is a European prospective multicentric observational cohort study. We considered all patients, between January 2020 and November 2022, who met the inclusion criteria, with suspected primary ovarian/tubal/peritoneal cancer or those who, after neoadjuvant chemotherapy, had undergone initial or interval debulking surgery. A standardised reporting template was used while performing ultrasound, CT, WB-DWI/MRI, and surgery to calculate the PCI score. Reference standards were intraoperative findings and surgical outcome. Of the 279 patients recruited, 182 were included in the final analysis comparing the three imaging methods: ultrasound, CT and WB-DWI/MRI. The optimal cut-off for surgical PCI was > 13 with an AUC of 0.86 for predicting non-resectability. Both ultrasound and WB-DWI/MRI achieved an AUC of 0.79 and CT achieved an AUC of 0.73. Ultrasound was non-inferior to CT (p = 0.012) but did not show to be non-inferior to WB-DWI/MRI (p = 0.142). Agreement between ultrasound and surgical findings was very high (0.94), between CT and surgical findings and between WB-DWI/MRI and surgical findings was high (0.86). This is the first prospective multicentric study evaluating the performance of the PCI using ultrasound, CT, and WB-DWI/MRI. Ultrasound is non-inferior to CT in predicting non-resectability in tubo-ovarian cancer patients and is the best imaging method in determining preoperative PCI when performed by experienced examiners in dedicated oncological centres.