Peritoneal metastasis histological grade independently predicts outcome in pseudomyxoma peritonei treated with curative surgery.

BACKGROUND

Pseudomyxoma Peritonei is characterised by peritoneal metastasis from appendiceal mucinous neoplasms (AMN). The PSOGI classification (2016) categorises PMP into acellular mucin (AM), low-grade mucinous carcinoma peritonei (LGMCP), and high-grade mucinous carcinoma peritonei (HGMCP). This study aimed to determine long-term prognosis based on this classification.

MATERIALS AND

METHODS

Pathology review from PMP patients with AMNs undergoing cytoreductive surgery and heated intraperitoneal chemotherapy (CRS + HIPEC) with curative intent over a 15-year period (2006-2021) was undertaken. Patients underwent standardised surveillance. Cox proportional hazards regression models, log-rank test, and Kaplan-Meier method were used to assess overall (OS) and disease-free survival (DFS) based on histopathological peritoneal metastasis grade. DFS was only calculated for patients who had a complete cytoreduction.

RESULTS

290 PMP patients were identified (AM = 34%, LGMCP = 59%, HGMCP = 7%) with median follow-up of 49 months. Median age was 59 years (range: 22-79), M: F of 1:2.5, peritoneal cancer index median of 18 (range: 0-39). Univariate OS hazard ratio (HR) is 2.75 for LGMCP vs AM (95% CI: 1.05 -7.21, p < 0.040) and 14.29 for HGMCP vs AM (95% CI: 3.92- 52.11, p < 0.001). DFS HR = 5.15 for LGMCP (95% CI: 2.19-12.10, p < 0.001) and 4.16 for HGMCP (95% CI: 1.03-16.80, p < 0.045) with an overall peritoneal metastasis p value < 0.001. Multivariate OS analysis showed that peritoneal histology for HGMCP remained a significant predictor of poor prognosis for OS (HR: 5.54, 95% CI: 1.32-23.25, p = 0.019), whilst LGMCP did not demonstrate a significant association (HR: 1.59, 95% CI: 0.59-4.26, p = 0.359).

DISCUSSION: Peritoneal metastasis histopathological grade predicts outcome for patients with PMP from AMN following CRS + HIPEC independent of primary histology.