... transform into the neoplastic nodule, composed of cells phenotypically similar to those of the foci, yet larger in size. Later still is the development of hepatocellular carcinomas. Foci of altered hepatocytes. Foci are microscopic lesions, distinguishable from healthy liver by various phenotypic characteristics. They are typically located in the periphery or intermediate region of the liver lobule, but may later progress to the centrilobular region [2]. Foci have been observed following the treatment of rats and mice with various carcinogens and hence have been used as markers in the identification of potential carcinogenic substances, [3]. Foci have also occurred in rats following x-irradiation [3] and in woodchucks infected by the woodchuck hepatitis virus [3]. An age-dependent increase in the occurrence of foci has been observed in control rats of several strains, particularly in aged rats [2]. An extremely high spontaneous incidence is observed in Fischer 344 rats, which may reach up to ...

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