Cellularity of mucus is a prognostic variable in low-grade appendiceal mucinous neoplasms.

For peritoneal metastases from a primary appendiceal mucinous neoplasm to exist, the thin wall of the appendix must perforate to allow mucus or mucus plus tumor cells to gain access to the peritoneal spaces. The proportion of specimens containing tumor cells within mucus as compared to mucus only outside the appendix may have prognostic significance. The histopathology of tumor masses was determined from the specimens resected at the cytoreductive surgery (CRS). The presence versus absence of tumor cells in mucus and the proportion of specimens with tumor cells was determined and correlated with the overall survival of these patients. In 418 patients with a complete cytoreduction for a low-grade appendiceal mucinous neoplasm (LAMN), the cellularity of all resected specimens was determined. The hazard ratio of overall survival of patients whose specimens had no cells as compared to specimens with cells in mucus by histology was 4.41 (1.61, 12.1) (p = 0.0039). If overall survival of patients with all specimens without tumor cells was compared to patients with specimens with 1-99 % tumor and compared to patients with 100 % of specimens with tumor cells, the hazard ratios were 4.3 (1.34, 13.8) (p = 0.0143) and 9.62 (2.93, 31.6) (p = 0.0002), respectively. The cellularity of mucus within the specimens removed by a complete CRS has strong prognostic implications in LAMN patients. LAMN with acellular specimens (LAMNa) as compared to LAMN with tumor cells in specimens (LAMNb) should be staged as different histologic subtypes of mucinous appendiceal neoplasms.