Primary liver cell carcinoma. New insight for a more correct approach to its classification.

Hepatocellular carcinomas, cholangiocellular carcinomas, and "indeterminate" forms have been studied by immunohistochemical detection of several antigens: alpha-fetoprotein and CEA, as well as type IV collagen, laminin, and keratin. While the first two antigens were variably detectable in different samples, in the poorly differentiated areas of hepatocellular carcinoma type IV collagen and laminin were both absent. These basement membrane glycoproteins constantly surrounded the cholangiocellular carcinoma tubular structures and were always present in those areas of the "indeterminate" group where the cells were organized as pseudoglandular or ductular aggregates. Keratin was absent in all cases of hepatocellular carcinoma, was variably detectable in the "indeterminate" neoplasms and was always present in cholangiocellular tumors. The neoplasias with mixed histopathological features usually showed morphological and biochemical biliary differentiation at the periphery, in contact with the collagenous stroma. We postulate that in some cases hepatocarcinoma cells undergo metaplastic transformation giving rise to cholangiocellular forms. Type IV collagen, laminin, and keratin seem to be accurate markers of phenotypical differentiation and show that a continuous phenotypical spectrum exists between hepatocellular and cholangiocellular entities.