Transcriptomic profiling of the intermediate cell carcinoma of the primary liver cancer

Introduction: Combined hepatocellular-cholangiocarcinoma (cHCC-CCA) is a mixed-type tumor of hepatocellular carcinoma (HCC) and intrahepatic cholangiocarcinoma (iCCA), which is classified into classical type (i.e., c-CHC) and intermediate cell type (i.e., i-CHC). c-CHC harbors both HCC and iCCA cells, whereas i-CHC is comprised of intermediate cell types lacking classical regions of HCC or iCCA cells. Notwithstanding the unique pathological feature of i-CHC, its molecular characteristics is not fully elucidated yet. Methods: To obtain molecular insights on the i-CHC, RNA-sequencing (RNA-Seq) and whole genome sequencing (WGS) profiling were performed on the tissues of i-CHC, HCC, and iCCA, respectively. Results: i-CHC showed unique transcriptomic features differing from HCC and iCCA, showing higher expression of Notch signaling and frequent splicing events of intron-retention (IR). Noticeably, we found that i-CHC had DNA-copy number loss and concomitant transcriptional suppression of METTL16, which may contribute to the aggressive progression of i-CHC via Notch activation. Conclusions: We suggest that i-CHC had unique transcriptomic features, providing new insights into the pathobiology of i-CHC.