Invasion Depth Measured in Millimeters is a Predictor of Survival in Patients with Distal Bile Duct Cancer: Decision Tree Approach

AJCC staging system is unreliable for predicting survival in distal bile duct (DBD) cancer patients, due to inter-observer variation. Measured depth of invasion (DOI) is suggested to be more accurate to predict patients' clinical outcome in extra-hepatic cholangiocarcinomas, but its significance in DBD cancer and cutoff values are still debatable. This study aimed to identify the optimal cutoff value of DOI in relation to prognosis in DBD cancer patients. Data of 179 patients with DBD adenocarcinoma treated in three institutions were investigated. Under microscopic review, DOI was measured. The relationships between the clinicopathological parameters and the groups based on DOI (3; 3-10; > 10 mm) were evaluated, and the survival times of each group based on DOI and T classification were compared. Deeply invading tumors exhibited a greater tendency toward the infiltrative type, high histological grade, AJCC stage, and pancreatic, duodenal, lymphovascular and perineural invasion. The measured DOI was significantly correlated with worse relapse-free and overall survival (all p < 0.05). In multivariate analyses, the DOI remained as one of the prognostic factors (all p < 0.05), while T classification was not a significant prognostic factor. The new prognostic models (low, intermediate, and high risk) that applied DOI and nodal metastasis showed significant difference in recurrence and survival rate (all p < 0.05). On the basis of the proposed cutoff value, the DOI could be clear and meaningful, overcoming the vagueness of the T classification for predicting clinical outcomes in patients with DBD carcinoma.