ObjectiveTo analyze the risk factors affecting prognosis of appendiceal adenocarcinoma using data from the Surveillance, Epidemiology, and End Results (SEER) database. MethodsThe patients pathologically diagnosed with appendiceal adenocarcinoma from 2005 to 2015 were extracted from the SEER database and then randomly divided into a training cohort and validation cohort at a 7∶3 ratio. The univariate and multivariate Cox regression analyses were performed in the training cohort to identify the independent risk factors for overall survival (OS) and cancer-specific survival (CSS). Based on these factors, a nomogram prediction model was constructed and subsequently validated. ResultsA total of 749 patients with appendiceal adenocarcinoma were enrolled, with 524 in the training cohort and 225 in the validation cohort. The multivariate Cox regression analysis identified that the T, N, M stages, and surgery as the independent prognostic factors for both OS and CSS. Additionally, the age and tumor size were the independent prognostic factors for OS and CSS, respectively. Based on these factors, the nomogram prediction models for OS and CSS were constructed. The C-index (95%CI) of the OS nomogram prediction model was 0.716 (0.689, 0.743) in the training cohort and 0.695 (0.649, 0.740) in the validation cohort. The C-index of the CSS nomogram prediction model was 0.749 (0.716, 0.782) and 0.746 (0.699, 0.793) in the training and validation cohorts, respectively. The calibration curves demonstrated a good agreement between predicted and observed outcomes for both OS and CSS. The area under the receiver operating characteristic curve (AUC) of the OS nomogram prediction model in predicting 3- and 5-year overall survival rate was 0.780 (0.739, 0.821) and 0.773 (0.732, 0.814) respectively in the training cohort, was 0.789 (0.726, 0.852) and 0.776(0.715, 0.837) respectively in the validation cohort. The AUC of the CSS nomogram prediction model in predicting 3- and 5-year cancer-specific survival rate was 0.813 (0.768, 0.858) and 0.796 (0.753, 0.839) respectively in the training cohort, was 0.813 (0.750, 0.876)and 0.811 (.750, 0.872) respectively in the validation cohort. ConclusionsThrough analysis of appendiceal adenocarcinoma patients from the SEER database reveals that advanced T, N, and M stages, as well as lack of surgery are significant risk factors for both OS and CSS. The constructed nomogram prediction models for OS and CSS, incorporating these risk factors, has a good prediction ability.