Impact of Mucin Cellularity and Distribution on Survival in Newly Diagnosed Patients with Low-Grade Appendiceal Mucinous Neoplasm Treated with Cytoreductive Surgery and Hyperthermic Intraperitoneal Chemotherapy

Background Low-grade appendiceal mucinous neoplasms (LAMN) are tumors that frequently present with peritoneal spread of either acellular mucin (AM) or cellular mucin (CM). We aim to determine how mucin types and distribution affect survival. Patients and Methods A retrospective cohort study was conducted using a prospective database. Newly diagnosed LAMN patients with AM versus CM treated with cytoreductive surgery/hyperthermic intraperitoneal chemotherapy (CRS/HIPEC) were compared. Postoperative pathology reports were reviewed to assess each involved abdominal zone. Survival was analyzed using the Kaplan-Meier method. Results Of 121 identified patients, 50 (41%) had peritoneal lesions with AM and 71 (59%) with CM. Peritoneal cancer index was lower in AM versus CM (mean: 19 +/- 13 vs 28 +/- 10, p = 0.004), but complete cytoreduction (CC) rates were similar (98% vs 96%, p = 0.642). The 5-year progression-free survival (PFS) was higher in AM versus CM (96% vs 69.8%, p = 0.002). CM patients had zones with both types of lesions: with and without cells. The CM subgroup analysis showed significant differences in 5-year progression-free survival (PFS) among patients with 1-3, 4-7, and 8-10 zones with cells (95.2%, 68.4%, and 35.7%, respectively, p < 0.001), but PFS was not affected by the number of zones with any lesion type. There was no difference in overall survival (OS) between groups. Conclusions Despite comparable CC rates after CRS/HIPEC, CM patients have shorter PFS than AM patients. In CM patients, more zones with cells, but not the total number of involved zones, negatively impact PFS. Mucin type does not impact OS. It is important to assess and report mucin cellularity in LAMN specimens.