Genomic and epigenomic architecture of hepatocellular carcinoma

Hepatocellular carcinoma (HCC) is one of the most common malignancies worldwide. Understanding of the intratumoral heterogeneity of HCC is instructive for developing personalized therapy and molecular biomarkers. We applied whole exome sequencing to a total of 63 samples from 11 patients to resolve the genetic architecture and subclonal diversification. Notably, spatial genomic diversity was found in all 11 HCC cases, with 33% of the driver mutations being heterogeneous. Temporal dissection of mutational signatures suggested that exogenous and endogenous factors have different contributions in shaping the mutational spectrum during the development of HCC. Moreover, we observed extensive intratumoral epigenetic heterogeneity in HCC, and showed that integrative analysis of both genetic and epigenetic phylogenies could generate more robust resolution of clonal architecture than single profiling approach. Our results also demonstrated prominent epigenetic subclonal diversification even in a stable HCC genome. Together, these findings highlight the widespread intratumoral heterogeneity at both genomic and epigenomic levels in HCC, and provide important molecular foundation for better understanding of the biology and pathogenesis of this malignancy. We examined a total of 22 tumor tissues and 4 morphologically-normal liver tissues (3 out of 4 were matched normal livers) from 5 HCC patients using Illumina Infinium HumanMethylation450K platform (Illumina, San Diego, CA).