Abstract

Epidemiological and experimental data have demonstrated that the process of carcinogenesis is progressive and multistage in nature. Model systems in animals exhibit this property of cancer development for several organ systems. The rat liver is one of the most extensively studied models of carcinogenesis. Multiple formats have been described for the analysis of cancer development in this organ, including the resistant hepatocyte selection regimens, the neonatal rat model and the partial hepatectomy model. The evolution of hepatic neoplasia is a slow process leading from the normal state via preneoplasia to benign and malignant neoplasia. On the histological level, hepatic preneoplasia usually emerges as foci of altered hepatocytes (FAH) which are perfectly integrated in the normal liver parenchyma and have no obvious neoplastic nature. The early emergence of FAH seems to be a general phenomenon of hepatocarcinogenesis in all species, no matter how this process has been elicited. The hallmark for the definition and detection of hepatic preneoplasia are biochemical and morphological changes in the hepatocellular phenotypes, which are neither uniform nor stable. In rodent liver treated with various chemical carcinogens, most of phenotypes have been shown to represent successive stages in an ordered sequence of cellular changes, progressing from glycogenic, clear and eosinophilic cell foci, through intermediate, mixed and basophilic cell populations, to hepatocellular adenomas and carcinomas, the fast growing variants of which consist of glycogen-poor, basophilic (ribosome-rich) cells. The identification of the placental isozyme of glutathione S-transferase (GST-P) as a highly expressed cytoplasmic protein during early carcinogenesis has led to its use as a marker of hepatic tumor development in early focal lesions, nodules and carcinomas. Different lesions have been suggested to represent preneoplastic conditions in human liver. They include large-cell change, small-cell change, foci of altered hepatocytes and dysplastic nodules. Experimental results suggest that multiple progressive factors are also involved in human hepatocarcinogenesis.

• Keywords: Liver neoplasms;Experimental;Neoplastic processes