Surveillance of low-grade appendiceal mucinous neoplasms for progression to pseudomyxoma peritonei: Results from a structured surveillance programme.

Aim: Low-grade appendiceal mucinous neoplasm (LAMN) of the appendix is a rare tumour that can progress to pseudomyxoma peritonei (PMP). There is a lack of standardization of surveillance following resection of LAMN as the progression rate to PMP is unclear. The aim of this study was to evaluate the rate of progression following resection of LAMN to PMP in a structured surveillance programme.

Method: Data for all patients referred for LAMN surveillance from 2013 to 2021 were retrospectively collected. The surveillance regime consisted of annual CT and tumour markers for a 5-year period. Patients who progressed to PMP were identified.

Results: Of the patients enrolled in surveillance following appendicectomy and LAMN diagnosis (65.1% female, median age 56 years), 83 had completed at least 1 year of surveillance (median follow-up 24 months). Of these, 6% (n = 5) showed disease progression during follow-up. The median time to progression was 23 months. Survival analysis revealed no statistically significant difference in progression with regards to T staging (p = 0.39), margin positivity (p = 0.11) or appendiceal perforation (p = 0.26). No patients with Tis disease developed PMP. A statistically significant difference in progression was seen in patients with M1b staging (p = 0.021) and in those with mucin beyond the right iliac fossa at diagnosis (p = 0.04).

Conclusion: The observed progression rate justifies the necessity of postappendicectomy surveillance in patients with LAMN, with the risk of progression being highest within the first 3 years of diagnosis. The described surveillance programme allows for early detection of subclinical progression to PMP.