Combined hepatocellular-cholangiocarcinoma with stem cell features, ductal plate malformation subtype: a case report and proposal of a new subtype.

In the current WHO blue book, combined hepatocellular-cholangiocarcinoma (C-HCC-CC) was classified into two types; classical type and type with stem cell features. The latter is extremely rare, and is subcategorized into the following three subtypes; typical subtype, intermediate cell subtype, and cholangiocellular subtype. Recently, intrahepatic cholangiocarcinoma (ICC) with features of ductal plate malformations (DPM) have been reported, and the ICC with DPM was proposed as a subtype of ICC. The author herein reports a case of C-HCC-CC with stem cell features. Characteristically, the CC element showed features of DPM. A 51-year-old man of HBV carrier was found to have high AFP. A laboratory test showed an elevated AFP (395 ng/ml, normal 9-10) and hepatitis B virus-related antigens and antibodies. Liver and ductal enzymes and PIVKAII were within normal ranges. Imaging modalities including CT identified a small liver tumor. Hepatocellular carcinoma (HCC) was suspected, and the resection of the hepatic tumor was performed. Grossly, the liver tumor is well-defined white solid tumor measuring 22x16x23 mm. Microscopically, the tumor was a C-HCC-CC, and was composed of following three elements: well differentiated HCC, well differentiated cholangiocarcinoma (CC), and intermediate tumor element. Characteristically, the CC cells formed tortuous markedly irregular tubules with intraluminal cell projections, bridge formations, intraluminal tumor biliary cells; such features very resembled the ductal plate (DP) and DPM. Immunohistochemically, the cells of CC element were positive for stem cell antigens (KIT (CD117), CD56, EMA, CD34), HepPar1, EpCAM, cytokeratin (CK) CAM5.2, AE1/3, CK34BE12 (focal), CK7, CK8, CK18, CK19, CA19-9, p53, MUC1, MUC2, MUC5AC, MUC6, and Ki-67 (labeling=25%). They were negative for CEA, CK5/6, CK20, NSE, chromogranin, synaptophysin, and p63. No mucins were found by histochemically. The background liver showed chronic hepatitis B (a1, f3). Very interestingly, many DPMs were scattered in the non-tumorous parenchyma. This type of C-HCC-CC with DPM features has not been reported. The author herein proposes that this tumor should be included or added in the C-HCC-CC subtype as C-HCC-CC with stem cell features, DMP subtype.