View of the regulatory use of rat liver foci data in the Federal Republic of Germany

Problems in consideration of rodent hepatocarcinogenesis for regulatory purposes

Hepatoproliferative lesions of rodents are frequently reported in petitions containing pathology data from chronic toxicity and carcinogenicity studies submitted to the Center for Food Safety and Applied Nutrition of the Food and Drug Administration. The Pathology Branch of the Office of Scientific Analysis and Support evaluates these data, which are submitted in support of the safe use of food additives, color additives, and other regulated products. Data are reviewed for the adequacy of the information provided, the terminology used to describe the reported lesions, and the overall scientific rationale used in interpreting the biological significance of the observed lesions. When questions arise during the review process, additional data, information, or clarification are sought from the petitioner. Microslides may be requested from the petitioner so that an independent evaluation of the lesions may be conducted. Several examples of recent evaluations of hepatoproliferative lesions are presented to illustrate some of the problems encountered during the review process and to demonstrate the procedures and approaches used in the evaluation of hepatocellular lesions within the center.

Morphology and incidence of hepatic foci of cellular alteration in Sprague-Dawley rats

Morphology and incidence of altered hepatocellular foci (AHF) were evaluated in standard H&E-stained liver sections from 3 groups of control Sprague-Dawley (SD) rats (initially 70/sex/group) used in 2 2-yr carcinogenicity studies. All AHF observed could be classified as basophilic, eosinophilic, clear, vacuolated, or mixed types using criteria applied previously to the Fischer-344 (F-344) rat. Some eosinophilic foci were large and posed a diagnostic challenge in differentiation from hepatocellular adenoma. Rats were arbitrarily divided into 3 classes by age at death: 14-17, 18-23, and 24-26 mo. As reported for F-344 rats, the incidence of SD rats with AHF increased with age, and males with eosinophilic foci predominated over males with basophilic foci whereas the opposite held true for females. Mean incidence of rats with AHF at 18-23 mo was 28 and 38% for males and females, respectively, and at 24-26 months was 68 and 71%, respectively. These data indicate a strikingly lower incidence of spontaneous AHF in SD rats than that reported for F-344 rats.