Fig. 3

a Microscopic findings of the tumor. Low magnification shows crowded, back-to-back tubulare structures (left side; adenocarcinoma) and parts of tubulocystic formations embedded in dense fibrous stroma (center; biliary adenofibroma) with adjacent normal liver parenchym (right side) (H&E × 20). The black circle indicates the bengin part of tumor (bililary adenofibroma) and the blue circle the malignant part of tumor (adenocarcinoma). These two different parts of tumor were marked on the histological slide for subsequent dissection. b At higher magnification, the cysts lined by a bland cuboidal single layer to columnar epithelium of the biliary phenotype with uniform nuclei without feature of malignancy; biliary adenofibroma (H&E × 400). c The areas of macroscopically solid appearance shows irregular pattern with crowded, anastomosing tubules. The nuclei closely packed, pseudostratified with heterogeneously distributed chromatin and prominent nucleoli; adenocarcinoma (H&E × 400). d Focal, the neoplasm shows a complex architecture, composed of pseudopapillary and cribriform-like tubules in a dense stroma; adenocarcinoma (H&E × 100). e In the peripheral area reveals irregularly glandular structures infiltrate the adjacent liver parenchyma; adenocarcinoma (H&E × 200). f Ki67 proliferation index in benign part of the tumor (biliary adenofibroma) less than 10 % (Ki67 staining × 200). g Ki67 proliferation index in the malignant part of the tumor (adenocarcinoma) significantly increased to 20–30 % (Ki67 staining × 200)