eP175 - Conditional Overall Survival in Appendiceal Adenocarcinoma: The Importance of Tumor Biology

Purpose/Background: Conditional overall survival (COS) is the probability of surviving additional years after a given follow-up interval. Appendiceal adenocarcinoma has a wide array of survival outcomes from long survivorships in indolent courses to very short disease-free survival in some cases. The significance of COS in appendiceal adenocarcinoma is largely unknown. The aim of the study was to investigate COS in appendiceal adenocarcinoma in a national cohort of patients.Methods/Interventions: The National Cancer Database was queried from 2004 to 2018 for adult patients with appendiceal adenocarcinoma managed with segmental colectomy. Inclusion criteria consisted of one-time cancer diagnosis, stage I-III, minimum of 12 regional lymph nodes, invasive disease component and known pathologic tumor and lymph node status. Patients with missing chemotherapy data, as well as nonspecific pathologic T stage were excluded. Survival probabilities were estimated and plotted using the Kaplan-Meier method. Cox regression models were utilized to estimate the effect of sociodemographic characteristics, clinicopathologic factors, and treatment on overall survival. Time was calculated from diagnosis to death. Patients still alive were censored at last follow-up.Results/Outcomes: A total of 3,185 patients were identified with stage I-III appendiceal adenocarcinoma who underwent right colectomy but only 2,232 patients were alive at 3 years. Of those, 47% were females, and the majority were under the age of 70 years (79%). Patients with well differentiated tumors were 30%, moderately 52%, and poorly about 18%. Mucinous pathology was identified in 40%, non-mucinous in 53%, while signet ring cell represented 7.4% of the histology groups. The overall survival for the cohort of 3,185 patients at time of surgery was 79% with the stage distribution being 89%, 83% and 60% for stage I, II and III, respectively. The overall survival conditional on surviving the first 3 years was 90%. Patients with stage I disease had a 95% COS, while those with stage II and III had 91% and 82% COS respectively (Figure 1). On multivariable analysis, histology of non-mucinous (HR 1.38 [1.06-1.81]) and signet ring cell (HR 1.77, [1.11-2.81]) adversely impacted the COS. Tumor grade did not significantly impact COS. Higher pathologic T and N stage were also found to be independently associated with worse COS, while adjuvant chemotherapy was not.Conclusion/

Discussion: In this national cohort of patients with appendiceal adenocarcinoma, we observed a significantly improved prognosis in patients reaching the 3-year mark, confirming COS to be a relevant endpoint in cancer survivorship. The pathologic T and N stages also maintained their prognostic value in COS, thus could reliably assist in counseling patients about their long-term outcomes. Patients with signet-ring cell histology had dismal COS, suggesting that this subgroup should be considered for more intense surveillance protocol.Comparison of the overall survival and conditional overall survival in appendiceal adenocarcinomaThe solid curve represented the overall survival of 79% in 3,185 patients over the course of 10 years. The dash line represented the conditional overall survival of 90% of 2,232 patients who survived the first three years.