Rising Incidence of Appendiceal Mucinous Adenocarcinoma in the United States: A SEER Analysis (2000–2022)

Appendiceal mucinous adenocarcinoma is an uncommon gastrointestinal malignancy with increasing recognition in recent years. We aimed to describe temporal and sex-based trends in incidence using national registry data.

This is a retrospective cohort analysis utilizing the Surveillance, Epidemiology, and End Results (SEER) 8 registries (2000–2022). Frequency analysis was performed to determine annual case counts stratified by sex. Cases were identified using ICD-O-3 histology code 8480/3 (mucinous adenocarcinoma) and site code C18.1 (appendix). Only malignant cases with known age were analyzed.

A total of 1568 cases were identified {Males = 706 (45%), Females = 862 (55%)}. The annual number of cases markedly increased from 24 cases in 2000 to 199 cases in 2022, representing more than an eightfold rise over two decades. Female incidence was consistently slightly higher than male incidence throughout the study period. The majority of cases occurred in White patients aged 50 years and above. Stage remains the strongest predictor of survival. Localized tumors demonstrated excellent long-term survival (5-year OS = 84.9%), whereas distant disease retained a 5-year OS of only 55.1%. Regional involvement resulted in intermediate survival (68.0% at 5 years). No cases were identified in the in situ category, suggesting detection typically occurs after invasion. Most patients underwent surgical management, while chemotherapy utilization varied by stage.

The incidence of appendiceal mucinous adenocarcinoma has steadily increased over the last two decades, likely reflecting improved detection and registry reporting. Further studies are needed to explore demographic and stage-specific survival trends.

- OS: Overall Survival.