Impact of Mucinous Histology on the Prognosis of Stage I-III Adenocarcinomas of the Appendix: a Population-Based, Propensity Score-Matched Analysis.

BACKGROUND: Whereas the poor prognosis of signet ring cell adenocarcinomas of the appendix is well known, the significance of mucinous histology remains unclear. The aim of this population-based study was to evaluate if mucinous histology is an independent prognostic factor in appendiceal adenocarcinomas.

METHODS: Patients with stage I-III adenocarcinoma of the appendix who underwent surgery between 2004 and 2012 were identified in the Surveillance, Epidemiology, and End Results database. Overall survival (OS) and cancer-specific survival (CSS) were assessed using risk-adjusted Cox proportional hazards regression models and propensity score methods.

RESULTS: Overall, 980 patients with appendix cancer were included, of which 449 (45.8 %) had a mucinous histology. In an unadjusted analysis, the 5-year OS and CSS in patients with a mucinous adenocarcinoma (MC) was 76.8 % (95 % confidence interval (95 %CI): 72.1-81.7 %) and 81.0 % (95 %CI: 76.6-85.6 %), respectively, compared with 70.0 % (95 %CI: 65.1-75.3 %) and 76.2 % (95 %CI: 71.5-81.2 %) in patients with non-mucinous adenocarcinoma (NMC) (P = 0.082 and P = 0.368). In multivariable analysis, no impact on survival was observed for OS (HR = 1.22, 95 %CI: 0.89-1.68, P = 0.208) and CSS (HR = 1.21, 95 %CI: 0.84-1.74, P = 0.296). After propensity score matching, nearly identical survival rates were observed (OS: HR = 1.03, 95 %CI: 0.71-1.49, P = 0.881 and CSS: HR = 1.05, 95 %CI: 0.70-1.59, P = 0.803).

CONCLUSIONS: The present population-based, propensity score matched analysis shows that mucinous histology does not affect survival in stage I-III appendiceal adenocarcinoma patients. Therefore, the same treatment strategies can be applied for patients with NMC and MC of the appendix.