Mouse Hepatoblastomas: A Histologic, Ultrastructural, and Immunohistochemical Study

Abstract

Abstract.Hepatoblastomas from B6C3F1 and BALB/c mice were examined by light and electron microscopy and by immunohistochemical reactions for alpha-fetoprotein, keratin, and vimentin. Tumors occurred in one group of a chronic bioassay for the interaction of diet, genetic strain, and the carcinogen, 2-acetylaminofluorene. Tumors had several populations (including epithelial and mesenchymal cells) in various stages of differentiation. Neoplastic epithelial cells had features of embryonal hepatocytes, such as sparse cytoplasmic organelles, absence of glycogen, abundant free ribosomes, occasional bile canaliculi, and peroxisome-like dense bodies. Embryonal fibroblast-like cells had pleomorphic and folded nuclei with prominent perinuclear chromatin and dispersed cytoplasmic organelles. Fibroblast-like cells were surrounded by bundles of collagen fibrils. Intermediate or transitional types of cells were seen. No tumor cells were immunoreactive for mouse alpha-fetoprotein (AFP) antibody, unlike those in hepatocellular adenomas or carcinomas. Epithelial and mesenchymal tumor cells contained intermediate filaments throughout the cytoplasm; some of these cells stained for keratin but not for vimentin. These findings suggest that mouse hepatoblastomas are derived from bipotential liver blastema cells and are composed of a mixture of several cell populations.Hepatoblastomas occur spontaneously and have been induced by chemical treatment in several strains of Distinctive histological features of these tumors, described by Turusov and colleagues in 1 973,42 included tumors diagnosed previously as hepatoblast~mas,~O poorly differentiated cholangiocarcinomas,29 cholangi~ma,~~ and an unusual tumor.4 We are not aware ofreports of hepatoblastomas in mice since 1973, except a case with squamous differentiati~n~~ and N-nitrosodiethylamine-induced hepatobla~tomas.~~ The existence of mouse hepatoblastoma in aged animals is still controversial, and its cell of origin is obs~u r e .~,~~The present study defines the detailed morphologic characteristics of this tumor by histological and ultrastructural observations together with immunohistochemistry for alpha-fetoprotein (AFT), keratin, and vimentin. Materials and Methods AnimalsMice used were part of a study conducted at the National Center for Toxicological Research (NCTR) to compare incStCrlfC3H/Nctr), raised at the NCTR. Diets were NIH-07 and AIN-76A, fed ad libitum. The carcinogen was 2-acetylaminofluorene (2-AAF) incorporated in the diets (Table 1). The study included 96 mice of each sex and strain at each dose group. Design for the AIN diet-and the NIH diet-fed groups were identical (Table 1). Animals were lulled after 24 months or when they became moribund by exsanguination under ether anesthesia.

Immunohistochemical Characterization of Hepatoblastomas in B6C3F1 Mice Treated with Diethylnitrosamine and Sodium Phenobarbital.

“…The reason for the discrepancy with the present results remains unclear, but the negativity of our mouse HBs for keratin, predominantly of higher molecularweight, might point to their being less-differentiated. Unlike to human HBs which are observed only in infancy or childhood, mouse HBs are usually observed at the latestage of chemical hepatocarcinogenesis studies and seem to grow later than HCAs or HCCs [3,5,19,32]. In this study, nearly half of HBs were observed in and/or adjacent to HCAs or HCCs, in line with the previous reports suggesting an origin from hepatocellular lineage.…”

“…In the present immunohistochemical examinations, mouse HBs were found not to react with antibodies against keratin, AFP, ALB or vimentin. Nonoyama et al [19] earlier reported 7 of 16 mouse HBs with squamous metaplasia to show positive reactions for keratin. Differentiation into ductal structures has also been described [12,20].…”

“…Mouse HBs can be induced by certain chemicals in some strains [10,19]. For example, Diwan et al [4,5] reported a high incidence in D2B6F1 mice administered DEN and PB.…”

“…Mouse HBs, however, lack a variety of subtypes and are histologically less differentiated. Previous immunohistochemical examination of the tumors revealed frequently positive for keratin, but no other specific immunoreactivity has been demonstrated so far [12,19]. Although several pathways can be conceived in the development of mouse HBs, no clear answer has been available so far due to their poorly differentiation.…”

“…Mouse hepatoblastomas (HBs) are rare, but occur spontaneously in aged animals or can be induced by certain chemicals in some strains [6,7,10,19,32]. Histologically, mouse HBs are well demarcated from surrounding normal tissues or hepatocellular neoplasms.…”