A novel pathology-based preoperative risk score to predict distant and locoregional residual disease and survival for incidentally discovered gallbladder cancer: A 10-institution study from the US Extrahepatic Biliary Malignancy Consortium.

202 Background: T-stage alone is currently used to guide treatment for incidentally discovered gallbladder cancer. We aimed to develop a more robust predictive model for discovering distant or locoregional residual disease at the time of re-resection. Methods: All patients with incidentally discovered gallbladder cancer who underwent re-resection at 10 institutions from 2000-2015 were included. We utilized routine pathology data from initial cholecystectomy to create a gallbladder cancer predictive risk score (GBRS) for finding distant or locoregional residual disease at re-resection and predicting overall survival (OS). Results: Of 449pts with gallbladder cancer, 262 (58%) were incidentally discovered and underwent attempted re-resection. Advanced T-stage, grade, and lymphovascular (LVI) and perineural (PNI) invasion were all associated with increased rates of distant and locoregional residual disease, and decreased OS. Each pathologic characteristic was assigned a value (T1a: 0, T1b: 1, T2: 2, T3/4: 3; well diff: 1, mod diff: 2, poor diff: 3; LVI neg: 1, LVI pos: 2; PNI neg: 1, PNI pos: 2), which were added for a total GBRS score ranging from 3-10. The scores were then separated into 3 risk groups (Low: 3-4; Intermediate: 5-7; High: 8-10). Each progressive GBRS group was associated with an increased risk of finding distant and isolated locoregional residual disease at the time of re-resection, and was associated with reduced median OS (Table). Conclusions: By accounting for pathologic variations within each T-stage, this novel predictive risk-score redistributes T1b, T2, and T3 disease across separate risk-groups and more accurately identifies patients with incidentally discovered gallbladder cancer at risk for distant and locoregional residual disease, and decreased long-term survival. This score may help to better optimize treatment strategy for patients with incidentally discovered gallbladder cancer. [Table: see text]