Correlation of two AgNOR counts with Ki-67 labeling index: a study in fine-needle aspirates of lymphoproliferative disorders and breast carcinoma.

The Ki-67 antibody binds to nonresting cells where Ki-67 labeling index (KLI) reflects proliferative activity (PA). The argyrophilic nucleolar organizer regions (AgNOR) counts have been correlated to ploidy and/or PA. Two AgNOR counting methods distinguish ploidy from PA. The first count is the mean AgNOR count (mAg-NOR) which correlates with ploidy. The second is the percentage of nuclei with > or = 5 AgNORs/nucleus (pAgNOR) which reflects PA. To explore this relationship, we separately stained smears of 20 fine-needle aspirates (FNAs) of lymphoproliferative disorders (n = 12) and breast carcinomas (n = 8) for AgNOR and Ki-67. We also double-stained 10 of the smears for both AgNOR and Ki-67. The correlation of pAgNOR counts and KLI was statistically significant (P < 0.0001) whereas it was not between mAgNOR and KLI (P = 0.13). Additionally, using the double stain, the Ki-67 negative cells had an AgNOR granule range of 1-3/nucleus with a mean of 1.33 (+1.86 SD). The Ki-67 positive cells showed an AgNOR granule range of 2-12/nucleus with a mean of 4.15 (+/- 1.02 SD) (P < 0.0002). We thus conclude that pAgNOR is a more reliable indicator of PA than mAgNOR and that four AgNORs/nucleus is an acceptable number differentiating proliferating from resting cells.