Proliferating cell nuclear antigen expression in rat glioma model: comparison with bromodeoxyuridine labeling index

The usefulness of proliferating cell nuclear antigen (PCNA) immunostaining for estimating the growth fraction in glial tumors was evaluated in ethylnitrosourea-induced rat gliomas. The PCNA labeling index was compared with the bromodeoxyuridine (BrdU) labeling index, using alternate serial sections fixed either in 10% formalin or in periodonate-lysine-paraformaldehyde (PLP). The PCNA labeling index was significantly correlated with the BrdU labeling index if cells with only faint PCNA staining were excluded. Differences in PCNA staining were noted between the two fixatives. The number of PCNA-positive cells in PLP-fixed material was greater than in 10% formalin-fixed material, but showed a poorer correlation with BrdU labeling index. Over-fixation in formalin reduced the number of positive cells. Although peritumoral tissue did not exhibit overexpression of PCNA, the ependymal lining was weakly stained even in areas distant from the tumor. PCNA labeling index is a useful method to estimate the growth fraction when the materials are processed in a controlled way. When clinical specimens with uncertain preparation are used, care is required in interpreting the results.