PROLIFERATING CELL NUCLEAR ANTIGEN EXPRESSION IN WISTAR RAT LIVERS - A RETROSPECTIVE IMMUNOHISTOCHEMICAL STUDY OF NORMAL AND NEOPLASTIC LIVERS

Formalin-fixed, paraffin-embedded liver specimens from 27 2-year-old W istar rats, including 10 normal livers, 11 hepatocellular adenomas, 2 hepatocellular carcinomas, and 4 cystic cholangiomas, were immunostain ed using the streptavidin/peroxidase method and the PC10 monoclonal an tibody (Mab), which recognizes an epitope on the proliferating cell nu clear antigen (PCNA). The following PCNA labeling index (LI) mean valu es were found for the above four groups of liver specimens: normal liv ers, 0.43 +/- 0.31 %; hepatocellular adenomas, 1.51 +/- 0.59 %; hepato cellular carcinomas, 24.80 % +/- 10.28 %; and cystic cholangiomas, 0.6 1 +/- 0.21 %. Our findings indicate that PCNA LI clearly separates liv er malignancies from other benign liver tumors, as well as from normal , non-neoplastic, liver tissues. Although the mean PCNA LI values seem ed to reflect histological grading (i. e. normal, neoplastic benign, n eoplastic malignant), overlapping between normal livers and hepatocell ular adenomas was observed in five cases (i. e. in 2 normal livers and 3 hepatocellular adenomas, where the PCNA LI values varied between 0. 74 % and 0.96 %). It thus appears that PCNA immunohistochemistry repre sents a promising tool for investigating liver cell proliferation in l aboratory rats, and permits distinguishing between benign and malignan t liver parenchymal tumors.