A Retrospective Case Control Study of Ductal Plate Malformation-like Features in Consecutive 200 Autopsies

Histopathological evidence of intrahepatic cholangiocarcinoma occurring in ductal plate malformation: A clinicopathologic study of 5 cases

Ductal plate malformations (DPM) arise from abnormal remodeling of the embryologic ductal plate of the liver. Malignant transformation of DPMs to intrahepatic cholangiocarcinoma (iCCA) has been reported in very rare instances but is viewed with some skepticism. We report the clinicopathological findings in five cases of iCCA, occurring in liver with DPM-like features. All tumors were less than 5 cm, often presented as stage T1a tumors. Histologically, a typical tumor showed a vague multinodular architecture with larger, irregular, tortuous glandular structures with microcystic dilation, intraluminal fibroepithelial projection, and bridge/island formation. The tumor cells were relatively small, bland, and without obvious pleomorphism. Interestingly, DPM presented as a histopathological transition sequence of definitively benign to biliary intraepithelial neoplasia (bilIN), then finally to iCCA. A complete pushing border, with entrapped portal tracts at the edge of the main tumor, suggested a replacing growth pattern. There was gradually increased expression of Ki-67 and p53 in these transition phases from benign to bilIN then to iCCA with DPM-like features. The neoplastic epithelium exhibited immunoreactivity in EpCAM, MUC1, NCAM, and CK19. KRAS mutation was found in 2 of the 5 iCCA cases with DPM-like features. Multifocal DPMs or VMCs with bilIN were dispersed in the non-tumor liver parenchyma in 3 of the 5 cases. The neoplasm was interpreted as iCCA arising in DPM, which may have originated from small bile duct or hepatic precursor cells. More studies are needed to verify this scarce entity and its premalignant properties.

Diversity in cell differentiation, histology, phenotype and vasculature of mass-forming intrahepatic cholangiocarcinomas

AIMS

Mass-forming intrahepatic cholangiocarcinomas (MF-iCCAs), involving small bile ducts, bile ductules or canals of Hering, remain treated as a single entity. We aimed to examine the diversity in histology, phenotype and tumour vasculature of MF-iCCAs.

METHODS AND RESULTS

Based on morphology and immunophenotype, we classified MF-iCCAs into small bile duct (SBD), cholangiolocarcinoma (CLC), ductal plate malformation (DPM) and hepatocellular carcinoma (HCC)-like subtypes. Genetic correlations among the histological subtypes were examined by multi-region tumour sequencing. Vasculatures and other clinicopathological features were compared among tumour groups with various proportions of the histological subtypes in 62 MF-iCCAs. Cases of pure SBD, CLC, DPM and HCC-like subtypes numbered 18 (29%), seven (11.3%), none (0%) and two (3%), respectively; the remaining 35 (56.4%) cases comprised several components. Genetic alterations, isocitrate dehydrogenase (IDH)1/2, KRAS, TP53, polybromo-1 (PBRM1) and BRCA1-associated protein 1 (BAP1), were shared among SBD, CLC, DPM and hepatoid components within a tumour. We uncovered distinct vascularisation mechanisms among SBD, CLC and DPM subtypes with a prominent vessel co-option in CLC tumours. iCCA with a DPM pattern had the highest vascular densities (mean microvascular density,140/mm² ; arterial vessel density, 18.3/mm² ). Increased CLC component was correlated with longer overall survival time (r = 0.44, P = 0.006). Pure SBD tumours had a lower 5-year overall survival rate compared with MF-iCCA with CLC pattern (30.5 versus 72.4%, P = 0.011).

CONCLUSIONS

MF-iCCAs comprise four histological subtypes. Given their sharing some driver gene alterations, indicating they can have a common cell origin, SBD, CLC and DPM subtypes, however, differ in cell differentiation, histology, phenotype or tumour vasculature.