Fig. 2

a Cuboidal to short columnar tumor cells were arranged in tubuloglandular structures, and some tubules dilated to cysts. These tubulocystic structures set in a fibrous stroma (H&E × 100). b Bile-like materials were observed in some lumens of the tubulocystic structures (black arrow)(H&E × 100). c Apocrine-like changes were seen in some lining epithelial cells. d Irregular tubules were densely arranged, the tumor cells showed round nuclei with prominent nucleoli and distinct nuclear membrane (left side; adenocarcinoma). And invasive growth in the adjacent liver parenchyma (right side) could be seen (H&E × 100). e Ki67 proliferation index in the benign part of the tumor was less than 10% (Ki67 staining × 100). f Ki67 proliferation index in the malignant part of the tumor markedly increased to 20–30% (Ki67 staining × 100)