Incidence, treatment, and survival of patients with appendiceal adenocarcinomas and low-grade appendiceal mucinous neoplasms: linked Swedish national registry study.

Abstract

Background: Appendiceal adenocarcinomas and low-grade appendiceal mucinous neoplasms (LAMNs) are rare tumours. Much of the existing knowledge is derived from registry-based studies, particularly the Surveillance, Epidemiology, and End Results database in the USA.

Methods: This retrospective cohort study used data from the Swedish Cancer Registry, Swedish Cause of Death Registry, and the National Patient Registry to analyse demographic characteristics and outcomes of patients diagnosed with appendiceal adenocarcinoma or LAMN between 2005 and 2019. Kaplan-Meier survivor function, multivariate Cox regression analysis, standardized mortality ratio, and net survival were used to assess survival. Incidence was estimated by direct standardization from 2005 to 2019.

Results: In all, 1159 patients with appendiceal neoplasms were included, with a mean age at diagnosis of 63.3 years. The incidence of adenocarcinomas was stable, whereas the incidence of LAMNs increased from 2012 onwards. Patients with non-mucinous adenocarcinomas who underwent colonic resection had better survival outcomes than patients treated with appendicectomy alone. For mucinous adenocarcinomas, colonic resection did not improve survival outcomes compared with appendicectomy. Patients with non-mucinous adenocarcinoma, mucinous adenocarcinoma, or LAMN who underwent cytoreductive surgery and heated intraperitoneal chemotherapy (CRS-HIPEC) had favourable overall and net survival.

Conclusion: Colonic resection increased survival only for patients with non-mucinous adenocarcinomas. Since 2012, the incidence of LAMN has increased, most likely due to changes in diagnostic and coding practices, but the incidence of appendiceal adenocarcinomas has remained stable. The survival benefit of CRS-HIPEC is observed in a very specific patient population, emphasizing the importance of careful patient selection.