S209 Appendiceal Adenocarcinomas Are Associated With Better Prognosis Than Cecal Adenocarcinomas: A Population-Based Comparative Survival Study

Abstract

Introduction: The incidence of appendiceal cancer in the U.S. has increased over the past two decades despite stable rates of appendectomies. Although the appendix is embryologically derived from the cecum, appendiceal adenocarcinomas have distinct molecular profiles from those of cecal adenocarcinomas. However, treatment protocols are the same and differences in survival outcomes between these malignancies have not been compared extensively. To this end, we conducted a comparative survival analysis of appendiceal and cecal adenocarcinomas. Methods: Using the Surveillance, Epidemiology, and End Results (SEER) database, we identified individuals ≥30 years of age with appendiceal or cecal adenocarcinomas from 1975 to 2016. Demographic and clinical data, including sex, age at diagnosis, year of diagnosis, race, ethnicity, marital status, tumor histology, tumor stage, tumor grade, chemotherapy, surgery, and survival in months, was extracted using SEER*Stat software. Relative hazard ratios for death in the five-year period following diagnosis were calculated using multivariate Cox regression analysis, adjusted for other covariates. Survival was compared by Mantel-Haenszel Log-Rank test, and survival curves were generated using the Kaplan-Meier method. The p-value level of significance was set at < 0.05 for a two-tailed test. Data was analyzed using SAS 9.4 software and R. Results: We identified 16,738 appendiceal and 87,047 cecal adenocarcinomas. Male sex, age >60, earlier year of diagnosis, black race, and non-Hispanic ethnicity were independently associated with higher mortality rates (Table). Those who were divorced, separated, never married, or widowed had worse survivorship compared to married individuals. Non-mucinous histology and advanced stage and grade were associated with worse prognosis, while surgery and chemotherapy were associated with improved survival. Multivariate Cox regression analysis demonstrated significantly lower mortality in appendiceal adenocarcinomas (HR 0.61; p< 0.0001). The five-year cancer-specific and overall survival curves for appendiceal and cecal cancers are shown in Figure. Conclusion: In this first large comparative survival study of appendiceal and colon cancers, appendiceal adenocarcinomas were associated with improved survival compared to that of cecal adenocarcinomas. Further investigation of prognostic factors and molecular mechanisms of appendiceal cancers is needed to establish standardized treatment guidelines.Figure 1.: Cecal and appendiceal adenocarcinomas - cancer-specific and overall survival experience by site Table 1. - Demographic and clinical factors associated with five-year mortality following diagnosis of appendiceal or cecal adenocarcinoma using multivariate Cox regression analysis Parameter P-value Hazard Ratio 95% Confidence Interval Sex Male 1 Female < 0.0001 0.89 0.87-0.91 Age >60 1 ≤60 < 0.0001 0.78 0.76-0.80 Year of Diagnosis 2005-2016 1 1991-2005 < 0.0001 1.56 1.49-1.63 1975-1990 < 0.0001 1.25 1.22-1.29 Race White 1 Asian/Pacific Islander 0.0003 0.91 0.87-0.96 Black < 0.0001 1.13 1.10-1.17 Ethnicity Non-Hispanic 1 Hispanic 0.003 0.94 0.90-0.98 Marital status Married 1 Divorced < 0.0001 1.14 1.10-1.19 Separated 0.02 1.11 1.02-1.21 Never married < 0.0001 1.15 1.12-1.19 Widowed < 0.0001 1.21 1.18-1.24 Histology Non-mucinous 1 Mucinous < 0.0001 0.89 0.86-0.91 Stage Local 1 Regional < 0.0001 3.60 3.43-3.77 Distant < 0.0001 17.61 16.79-18.47 Grade I: Well differentiated 1 II: Moderately differentiated < 0.0001 1.32 1.26-1.37 III: Poorly differentiated < 0.0001 1.99 1.90-2.08 IV: Undifferentiated; anaplastic < 0.0001 2.11 1.96-2.28 Surgery Surgical excision 1 Biopsy only < 0.0001 3.55 3.38-3.74 No surgery or biopsy < 0.0001 5.39 4.87-5.97 Chemotherapy Chemotherapy 1 No chemotherapy < 0.0001 1.06 1.03-1.08 Site Cecum 1 Appendix < 0.0001 0.64 0.61-0.67