Reappraisal of classification of distal cholangiocarcinoma based on tumour depth

Background In the eighth edition of the AJCC cancer staging classification, the T system for distal cholangiocarcinoma (DCC) has been revised from a layer‐based to a depth‐based approach. The aim of this study was to propose an optimal T classification using a measured depth in resectable DCC. Methods Patients who underwent pancreatoduodenectomy for DCC at 32 hospitals between 2001 and 2010 were included. The distance between the level of the naive bile duct and the deepest cancer cells was measured as depth of invasion (DOI). Invasive cancer foci were measured as invasive tumour thickness (ITT). Log rank χ2 scores were used to determine the cut‐off points, and concordance index (C‐index) to assess the survival discrimination of each T system. Results Among 404 patients, DOI was measurable in 182 (45·0 per cent) and ITT was measurable in all patients, with median values of 2·3 and 5·6 mm respectively. ITT showed a positive correlation with DOI (rS = 0·854, P