Small but significant: Prognostic value of the small duct type in intrahepatic cholangiocarcinoma

This study aimed to evaluate the clinicopathological features, prognostic relevance, and classification accuracy of histological subtypes-the small duct type and the large duct type-in intrahepatic cholangiocarcinoma (iCCA) based on the WHO 5th edition criteria. A retrospective analysis was conducted on iCCA cases classified into the small duct type and the large duct type. Key pathological variables were identified using logistic regression and used to develop a random forest classification model. Survival outcomes were analyzed using Kaplan-Meier and Cox regression analyses. The random forest model, using nine significant pathological features, achieved an overall classification accuracy of 83 %. Mucin production, tumor grade, and intraepithelial lesion were among the most influential predictors. The small duct type was associated with significantly better overall survival (5-year rate: 57.6 %) and recurrence-free survival (46.6 %) compared to the large duct type (24.9 % and 20.6 %, respectively). Multivariable analysis confirmed the large duct type as an independent predictor of worse prognosis. Histological subtyping of iCCA holds important prognostic value. The small duct type is associated with a more favorable clinical course, supporting the integration of subtype-aware assessments into diagnostic and prognostic frameworks. These findings may inform future developments in computational pathology and personalized treatment strategies.