Novel staging system using carbohydrate antigen (CA) 19-9 in extrahepatic cholangiocarcinoma (ECCC) and its implications on overall survival (OS).

Abstract

4091 Background: Optimal management of ECCA patients with elevated CA19-9 remains undefined. We hypothesized CA 19-9 elevation as a marker of aggressive biology in ECCA and that inclusion of CA 19-9 in the staging may improve OS discrimination. Methods: Patients with ECCA with CA 19-9 levels reported to the National Cancer Database (years 2004-2015) were included. The patients were classified based on their CA19-9 levels and a new staging system was proposed. Based on the current knowledge, we considered 37 U/ml as our cut off. Kaplan Meier method was used to compare OS between the groups. The net reclassification improvement (NRI) model was used to assess the predictive improvement in the proposed survival model. Results: A total of 2100 patients met the inclusion criteria: 601 (32%) and 1436 (68%) had normal and elevated CA19-9 levels, respectively. Rates of chemo (p=0.16) and radiation therapy (p=0.07) were similar between groups, but patients with elevated CA19-9 were less likely to undergo resection. Resected patients with CA19-9 elevation had higher 30-day mortality (p=0.02) and lower median OS (p<0.01). Patients with elevated CA 19-9 levels had decreased stage-specific survival in all stages (p<0.01). On adjusted analysis, CA19-9 elevation independently predicted poor OS (HR: 1.67 [1.42-1.97]) with impact resembling nodal metastasis, positive resection margin, lymphovascular invasion, and non-receipt of surgery or chemotherapy (p<0.01). CA 19-9 included proposed staging system (Table) had a better OS discrimination over AJCC 7th edition. The new staging system had a concordance of 60% as opposed to 58% for the AJCC staging, leading to an improvement of 2% (p<0.01). NRI of 46% (95% CI: 39-57) indicates that the new staging system is substantially effective at re-classifying events at 12 months as compared to AJCC staging. Conclusions: Elevated CA19-9 was found to be an independent risk factor for mortality in ECCA and its inclusion in the newly proposed staging system markedly improved OS discrimination.[Table: see text]