DIFFERENTIAL IMAGE-ANALYSIS OF PROLIFERATING CELL NUCLEAR ANTIGEN (PCNA) EXPRESSION LEVEL DURING EXPERIMENTAL THYROID CARCINOGENESIS

Immunostaining of proliferating cell nuclear antigen (PCNA), which can be applied to routinely processed tissue sections, has extended the a pplications of cell kinetic studies. PCNA immunostaining intensity of cells varies among individual nuclei in tissue sections. To determine the changes in PCNA expression level during carcinogenesis, we employe d an image analyzer to evaluate PCNA staining intensity in diisopropan olnitrosamine (DIPN)-induced neoplastic lesions of rat thyroid glands. In the normal thyroid gland, only small numbers of cells showed weak PCNA expression. The percentage of PCNA-positive cells increased durin g carcinogenesis, i.e. hyperplasia, adenoma, and then carcinoma. Analy sis of PCNA staining intensity histograms revealed that the population of cells with stronger intensity increased during carcinogenesis, i.e . from adenoma to carcinoma. However, the percentage of cells with wea k PCNA staining increased in hyperplasia, and did not change in intens ity during further carcinogenic sequelae. These differences in PCNA ex pression level recognized by immunostaining intensity may reflect diff erent cell kinetics between the process of hyperplasia and that of dif ferentiation from adenoma to carcinoma.