Argyrophilic staining for nucleolar organizer region (AgNOR). A suitable methodology for differential diagnosis of breast lesions?

Argyrophilic (Ag) staining for nucleolar organizer regions (NORs) is now emerging as a useful means for confirmation and exclusion of malignancy, discriminating features being the number, morphology and distribution of AgNORs. We have put the validity of this method to the test by comparing a series of potentially problematic breast lesions: atypical epitheliosis (n = 22) versus carcinoma in situ (n = 16) and sclerosing adenosis (n = 11) versus invasive carcinoma (n = 20). Malignant epithelial cells contained, in general, more AgNORs than benign proliferation but there was overlapping and the method could reliably differentiate only between sclerosing adenosis and invasive carcinomas (P less than 10(-6). In the latter, irregularity and intranuclear dispersal of AgNORs were prominent features. The conclusion is drawn that increased AgNORs counts may be associated with aggressive biological behaviour but this it not an absolute marker of malignancy in the breast.