CA 19-9 to peritoneal carcinomatosis index (PCI) ratio is prognostic in patients with epithelial appendiceal mucinous neoplasms and peritoneal dissemination undergoing cytoreduction surgery and intraperitoneal chemotherapy: A retrospective cohort study.

Background: Serum tumour levels have been shown to be prognostic in patients with epithelial appendiceal mucinous neoplasms with peritoneal dissemination (pseudomyxoma peritonei (PMP)). A singular index which incorporates both tumour activity (as depicted by serum tumour marker levels) and tumour volume (as depicted by peritoneal carcinomatosis index (PCI)), may give a more precise surrogate of tumour biological behaviour. The prognostic implication of this index has not yet been reported.

Methods: A retrospective cohort study of all patients with PMP managed from 1996 to 2016 with cytoreductive surgery (CRS) and intraperitoneal chemotherapy (IPC) was performed by analysing the survival effect of the ratio of preoperative serum CEA, CA19.9 and CA125 to PCI.

Results: Three hundred and eighty-six patients were included. In patients with low-grade PMP, elevated CA19-9/PCI ratio resulted in poorer median overall survival times (104 months vs NR, 95%CI 83 - NR, log-rank p < 0.001) and was an independent predictor of reduced overall survival on multivariable analysis (adjusted HR 5.60, 95%CI 1.60-19.68, p = 0.007). In patients with high-grade PMP, no statistically significant difference in survival was recognised.

Conclusion: CA19-9/PCI ratio is an independent prognostic factor for overall survival in patients with low-grade PMP undergoing CRS and IPC. By accounting for both tumour activity and tumour volume simultaneously, this novel index behaves as a surrogate of tumour biology and provides a useful adjunct for decisions regarding treatment allocation in this patient group.