The correlation of two argyrophilic nucleolar organizer region counting methods with bromodeoxyuridine-labeling index: a study of metastatic tumors of the brain.

Bromodeoxyuridine (BrdU) is a thymidine analog that is incorporated into cellular DNA in the synthetic phase. The BrdU-labeling index (BLI) thus reflects the S-phase fraction. The argyrophilic nucleolar organizer regions (AgNORs) are silver-stained granules that have been correlated with ploidy and/or S-phase fraction. Two AgNOR counting methods have been proposed to distinguish between ploidy and S-phase fraction: the mean AgNOR (mAgNOR) count (the mean number of AgNOR granules in 100 cells), which is believed to reflect ploidy, and the AgNOR proliferative index (pAgNOR) (the percentage of cells exhibiting five or more AgNOR granules per nucleus), which is believed to reflect S-phase fraction. To evaluate the latter hypothesis we studied 19 tumors metastatic to the brain in patients who had received preoperative low-dose BrdU injections. Formalin-fixed, paraffin-embedded sections of the resected tumors were stained using the indirect immunoperoxidase technique and a monoclonal antibody to BrdU. The BLI was determined by counting 1,000 tumor cells in each case; AgNOR silver staining was performed on sections of the same blocks studied for BLI. The correlation between pAgNOR counts and BLI was statistically significant (r = .649, P = .003). No statistically significant correlation could be obtained between mAgNOR counts and BLI (r = .421, P = .17). We conclude that the pAgNOR count can reliably reflect the proliferative activity of cells. The method can prove beneficial in situations in which cell kinetic analysis is needed and in which invasive procedures, such as BrdU injection, are not feasible or are contraindicated.