Nucleolar organizer regions relate to growth fractions in human breast carcinoma

An argyrophil stain for nucleolar organizer regions (NORs) has recently been applied to paraffin sections of human tissues. This report describes a positive relationship between the mean numbers of AgNOR sites per nucleus and tumor growth fraction, as determined by immunostaining with the monoclonal antibody Ki-67, in 83 malignant breast tumors (P < .01). This relationship supports recent suggestions that the NOR count may reflect cell synthetic activity and hence, proliferation. AgNOR counts correlated inversely with immunocytochemically assessed estrogen receptor content (P < .002), but there was no relationship between the AgNOR count and primary tumor size, histologic grade, axillary node status, or patient age. A significant difference (P < .00001) was found between the AgNOR counts in 64 benign breast lesions (mean, 2.05) and 85 malignant breast neoplasms (mean, 5.46). The limitations of the silver staining technique and the problems of reproducibility in AgNOR counting are detailed.