Abstract: Objective To explore the clinicopathologic features and prognosis of primary malignant tumors of the appendix,assess the factors affecting the prognosis,and provide a reference for the development of treatment programs and evaluation of patients'prognosis. Methods This analysis included cases of malignant tumors of the appendix reported to the National Cancer Institute's Surveillance,Epidemiology and End-results (SEER) program between 2004 and 2010.Adenocarcinoma,mucinous adenocarcinoma,signet ring cell carcinoma and neuroendocrine tumor were included according to WHO Classification of Tumors of the Digestive System (Fourth Edition).Data analysis was performed using IBM SPSS software for Windows,version 19.0.Disease-specific survival was calculated according to the Kaplan-Meier method,and differences between curves were tested by the log-rank test,using P<0.05 as the limit of significance.Cox's proportional hazard regression analysis was performed using a multivariate analysis to identify independent prognostic factors in cancer patients. Results Between 2004 and 2010,3 967 malignant tumors of the appendix were reported to the SEER program,of which 3 159 cases were included in the analysis.The annual age-adjusted incidence of cancer of the appendix was 0.7 cases per 100 000 people.The survival rate was inversely proportional to age;African Americans had a worse prognosis than others.The higher the degree of tumor invasion,the worse the prognosis was.The disease specific survival rate of patients with signet ring cell carcinoma was lower than that of other types of tumors in all histological types (P<0.001).The patients with neuroendocrine tumors had a better prognosis (P<0.001). Conclusion The demographics of patients with primary malignant tumors of the appendix vary by histological classification.The race,age of diagnosis,grade,and histological types,the extent of the tumor at the time of diagnosis and tumor size were independent prognostic factors for primary neoplasms of the appendix.