Histology of Recurrence Following CRS‐HIPEC for Low‐Grade Peritoneal Metastases From Mucinous Appendiceal Neoplasms

BACKGROUND: Low-grade (LG) mucinous carcinoma peritonei (LGMCP) arising from mucinous appendiceal neoplasms is typically treated with cytoreductive surgery and hyperthermic intraperitoneal chemotherapy (CRS-HIPEC). Although these patients can recur after CRS-HIPEC, the histology and outcomes of recurrence have not been well-documented. METHODS: A retrospective study of CRS-HIPECs from 2007 to 2024 at our institution was performed for patients with LG primary and peritoneal histology. Recurrence was defined as LG or high-grade (HG), with HG histology defined as high-grade mucinous carcinoma peritonei (HGMCP) or adenocarcinoma (AC). Overall (OS) and progression-free survival (PFS) were measured by Kaplan-Meier survival analysis. RESULTS: We identified 246 CRS-HIPEC procedures performed for LG peritoneal histology: 171 (69.5%) LGMCP, 69 (28%) acellular mucin, and six (2.4%) with benign peritoneal histology. Median follow-up time was 67 months (range 0.3-199.2 months). Seventy-six (30.9%) patients recurred: 39/61 (63.9%) had LG histology and 22/61 (36.1%) had HG histology. Median PFS was 166.8 months (95% CI 114.6-219). For those who recurred, PFS was no different for patients with LG versus HG recurrence (21.1 months (95% CI 11.6-30.6) vs. 21.4 months (95% CI 15.2-27.6); p = 0.53). Median OS was not reached and 10-year OS was 63.2% with LG recurrence versus 25.0% with HG recurrence (p = 0.07). CONCLUSION: Approximately one-third of patients undergoing CRS-HIPEC for LG peritoneal metastases from mucinous appendiceal neoplasms recurred; one-third of recurrences had HG histology. Those with LG recurrence trended improved survival versus HG recurrence. These findings impact patient counselling, management, and further investigation of risk factors and mitigation strategies.