(PM P4) Impact of Cellularity in Peritoneal Metastases on Survival in Patients with Low-Grade Appendiceal Mucinous Neoplasm (LAMN)

Objective. Low-grade appendiceal mucinous neoplasms (LAMN) are tumors which frequently present with peritoneal spread of either acellular (AM) or cellular mucin (CM). We aimed to determine how mucin type and distribution affect survival. Methods. A retrospective cohort study was conducted using a prospective database. Newly diagnosed LAMN patients with AM vs 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 with the Kaplan-Meier method. Results. Of 121 identified patients, 50 (41%) had LAMN with AM and 71 (59%) with CM. Peritoneal cancer index was lower in AM vs CM (21 vs 31, p=0.004), but complete cytoreduction (CC) rates were similar (98% vs 96%, p=0.64). The 5-year progression-free survival (PFS) was higher in AM vs CM (96% vs 69.8%, p=0.002). CM patients had both zones with epithelial cells and zones with only mucin. CM subgroup analysis showed significant differences in 5-year PFS between patients having 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 total number of altered zones containing cells and mucin. There was no difference in OS between any groups. Conclusion. Despite comparable CC rates after CRS/HIPEC, LAMN patients with CM have shorter PFS than AM patients. In CM patients, more zones with cells, but not the total involved zones, negatively impacts PFS. Mucin type does not impact OS. It is important to assess mucin cellularity in LAMN specimens.