Proposal of an optimal depth-based tumor classification in distal cholangiocarcinoma

Abstract

Introduction: The American Joint Committee on Cancer (AJCC), 8th edition, has revised the T system for distal cholangiocarcinoma (DCC) from layer-based to depth-based approach. The aim of this study was to propose an optimal T classification using a measured depth in resectable DCC. Method: Patients who underwent pancreatoduodenectomy for DCC at 32 hospitals between 2001 and 2010 were included. The distance between the basal lamina and the advancing cancer cells was measured as depth of invasion (DOI). The invasive cancer foci was measured as invasive tumor thickness (ITT). Log-rank χ2 was used to determine the cutoff points, and C-index was used to assess the survival discrimination of each T system. Results: Some 404 patients were included. DOI and ITT were measurable in 182 and all patients, and the medians were 2.3 and 5.6 mm, respectively. They both showed a strong positive correlation (correlation coefficient, 0.854), and the cutoff points of ITT were 1, 5, and 10 mm. The median survival time was significantly shortened with increase in ITT: 12.4 years for ITT< 1 mm, 5.2 years for 1≤ITT< 5 mm, 3.0 years for 5 ≤ITT< 10 mm, and 1.5 years for ITT≥10 mm . This 4-tier ITT classification exhibited the most favorable prognostic discrimination, compared to the T systems of AJCC 7th/8th editions (C-index: 0.6463, 0.6218, and 0.6243). Conclusions: ITT is a versatile approach for depth assessment in DCC. The 4-tier ITT classification with cutoff points of 1, 5, and 10 mm can be used as an optimal T system.