Malignant neoplasms of the appendix have different behavior based on their histologic subtypes in anecdotal series. Current staging systems do not capture the diversity of histologic subtypes in predicting outcomes.

We queried all patients with appendiceal malignancies captured in the Surveillance, Epidemiology, and End Results (SEER) database from 1973 to 2007. Tumors were classified as colonic type adenocarcinoma, mucinous adenocarcinoma, signet ring cell type, goblet cell carcinoid, and malignant carcinoid. We compared incidence, overall survival, and disease-specific survival for these tumors on the basis of patient, tumor, and therapy characteristics. Estimates from Cox proportional hazard modeling were used to predict hazard ratios for differing histologic subtypes with similar tumor, node, metastasis system (TNM) stages.

Of the 5672 patients identified, we included 5655 (99%) in our analysis. The 5-year disease-specific survival rates were 93% for malignant carcinoid, 81% for goblet cell carcinoid, 55% for colonic type adenocarcinoma, 58% for mucinous adenocarcinoma, and 27% for signet ring cell type. Predicted estimates of adjusted hazard ratios revealed an 8-fold difference between histologic subtypes for similar TNM stages.

Histologic subtype is an important predictor of disease-specific survival and overall survival in patients with appendiceal neoplasms. Addition of the histologic subtype to the TNM staging is simple and may improve prognostication.