Quantitative evaluation and stereological analysis of altered hepatocellular foci (AHF) were performed on hematoxylin and eosin-stained (H&E) liver sections from control Wistar rats from 9 2-yr carcinogenicity studies conducted between 1981 and 1991. Morphologic criteria previously described were used to classify AHF in H&E stained livers into basophilic, eosinophilic, clear, mixed, or vacuolated cell foci. Hepatocellular adenomas were seen in 1.6% of control rats and carcinomas were seen in 0.2%. AHF were diagnosed in 20% of control Wistar rats and were seen only in rats dying after 47 weeks. Basophilic foci were the most common AHF seen; incidences of tigroid and diffuse basophilic AHF were similar. Vacuolated foci were not identified in any rat. The mean number of AHF per cubic centimeter of liver was 101. The mean AHF volume varied from 0.002-0.048 mm3 and the mean volume fraction ranged from 0.005-0.026%. Compared to AHF in aged control Fischer 344 rats, AHF in control Wistar rats were fewer and smaller.
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