Frequency and risk factors for metastasis in newly diagnosed appendiceal carcinoma.

e16281 Background: Appendiceal carcinoma has an insidious clinical presentation, and these tumors are rarely suspected prior to surgery, potentially leading to late diagnosis. The aim of this study is to investigate the prevalence of metastatic disease at initial presentation and potentially associated sociodemographic characteristics. Methods: Patients were identified from the Surveillance, Epidemiology, and End Results (SEER) program using ICD-O-3 histology/behavior codes between 2010-2015. Logistic regression was performed to determine the association of metastasis at presentation with tumor subtype, adjusted for age, race, sex, insurance and marital status, grade, and tumor and nodal stage using the seventh edition of the American Joint Committee on Cancer (AJCC) staging system. Results: We identified a total of 3, 447 patients with known metastatic status. 38.4% had metastatic disease at diagnosis. Compared to colonic-type adenocarcinoma (CA), mucinous adenocarcinoma (MA) was associated with significantly higher odds of presenting with metastasis at diagnosis in unadjusted (OR 3.55; 95% CI [2.97-4.24]) and adjusted (OR 2.97 [2.26-3.89]) regression. Signet ring cell carcinoma (SC) also had higher odds in unadjusted (OR 3.91 [2.99-5.12]) and adjusted (OR 2.05 [1.33-3.15]) regression. Goblet cell carcinoma (GC) was associated with lower odds in unadjusted (OR 0.28 [0.21-0.37]) and adjusted (OR 0.58 [0.36-0.94]) regression. The table describes the association of tumor and nodal stage with metastasis at diagnosis. Women had higher odds in unadjusted (OR 1.59 [1.39-1.82]) and adjusted (OR 1.93 [1.55-2.39]) regression. 90.1% of CA, 84.2% of GC, 42.2% of MA, and 78.5% of SC patients with metastasis at diagnosis had extraperitoneal distant metastasis (M1b). Conclusions: A significant proportion of patients with appendiceal carcinoma had metastasis at diagnosis. Compared to CA, MA and SC were much more likely to present with metastasis at diagnosis, while GC was less likely. Women had almost twice the odds of presenting with metastatic disease as men. T4 and N2 stages showed much higher odds of metastasis at diagnosis compared to T1 and N0 stages, respectively. Surprisingly, T2 and T3 stages were associated with lower odds of metastasis at diagnosis than T1 stage.[Table: see text]