This study assessed the value of argyrophilic nucleolar organizer region (AgNOR) staining as a potential technique for the estimation of cell kinetics in conventional histology sections, in benign and malignant breast lesions. Using a silver staining technique and immunohistochemistry, the authors correlated the numbers of argyrophilic nucleolar organizer regions (AgNORs) and Ki67 scores in 70 breast carcinomas and 27 benign breast lesions. Epithelial cells in fibrocystic disease and fibroadenomas contained a mean of 2.65-6.8 small uniform AgNORs per cell, whereas malignant cells contained 4.6-26.9 frequently highly irregular AgNORs. In benign tissue, Ki67 scores ranged from 0 to 4%; in malignant tumors, Ki67 scores ranged from 3.0 to 98%. The correlation between AgNOR counts and Ki67 scores was highly significant (P less than 0.001). The authors concluded that AgNOR counts performed on routine formalin-fixed paraffin sections furnish significant kinetic information. Furthermore, the difference in AgNOR counts between benign and malignant tumors is such that they may be of diagnostic value.

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