Multiregional analysis of combined hepatocellular‐cholangiocarcinoma reveals histologic diversity and molecular clonality.

Combined hepatocellular‐cholangiocarcinoma (cHCC‐CC) is a rare type of liver tumour that exhibits both hepatocytic and biliary differentiation within the same tumour. The histology and genomic alterations of recurrent/metastatic cHCC‐CC are poorly understood. We selected six patients with cHCC‐CC whose recurrent or metastatic tumours were histologically confirmed. Four patients with classic cHCC‐CCs and two with intermediate cell carcinomas (ICs) were included. The clinicopathological features were evaluated, and next‐generation sequencing was performed in 17 multiregional and longitudinal tumour samples. The histology of recurrent/metastatic lesions of classic cHCC‐CCs was variable: hepatocellular carcinoma (HCC) was observed in one (25.0%) patient, cHCC‐CC in one (25.0%) patient, and cholangiocarcinoma (CC) in two (50.0%) patients. Among 13 samples from four classic cHCC‐CC patients, the most frequent pathological variants were TP53 (46.2%), TERT promoter (38.5%), ARID1A mutations (23.1%), and MET amplification (30.8%). In the sequencing analysis of each HCC and CC component, three (75.0%) of the four classic cHCC‐CCs shared pathogenic variants. A large proportion of mutations, both pathogenic and those of undetermined significance, were shared by each HCC and CC component. Regarding ICs, the ATM mutation was detected in one patient. In conclusion, the histology of recurrent/metastatic cHCC‐CCs was heterogeneous. Genomic profiling of classic cHCC‐CCs revealed similar genomic alterations to those of HCC. Considerable overlapping genomic alterations in each HCC and CC component were observed, suggesting a monoclonal origin. Genetic alterations in ICs were different from those in either HCC or CC, suggesting the distinct nature of this tumour. [ABSTRACT FROM AUTHOR]