Background Recently, the Liver Cancer Study Group of Japan (LCSGJ) staging system for intrahepatic cholangiocarcinoma (ICC) was followed by a proposal of the American Committee on Cancer (AJCC)/International Union Against Cancer (UICC) system. The present study aimed to assess the accuracy of both systems to predict survival after curative resection for mass-forming ICC and to establish a new staging system based on survival analysis results. The present study was conducted as a project study of the Japanese Society of Hepato-Biliary- Pancreatic Surgery. Methods Clinical data from 233 patients who underwent curative resection for mass-forming ICC were retrospectively reviewed. Survival analysis was performed to identify predictors of postoperative outcomes, and a new staging system was established. The survival stratification of our proposed system was compared with two previous staging systems. Results A N0M0 cohort analysis demonstrated that tumor size, tumor number, and vascular invasion were independently associated with survival after curative resection for mass-forming ICC, whereas serosal and periductal invasion were not. Of patients with nodal metastases, patients with T4 tumor had significantly lower overall survival rate than patients with T1, T2, or T3 tumor. Thus, we proposed a new staging system as follows: serosal invasion was excluded from the LCSGJ T categories, and patients with nodal metastases were divided into stage IVA or IVB according to T classification. The new system better stratified survival after curative resection for mass-forming ICC than the two previous systems. Conclusions The AJCC/UICC staging system failed to stratify the Japanese patients with mass-forming ICC. The new staging system provided better survival prediction in the patients who underwent curative resection for mass-forming ICC, although further studies are necessary to evaluate the impact of tumor size on survival.
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