AgNORs in benign, dysplastic, and malignant melanocytic skin lesions.

Nucleolar organizer regions (NORs) are loops of DNA situated on the short arms of acrocentric chromosomes 13, 14, 15, 21, and 22; they can be demonstrated in formalin-fixed paraffin-embedded sections by a one-step silver technique, the resulting black structures being termed AgNORs. We have applied the technique to 30 benign "banal" nevi (BN), 30 dysplastic nevi (DN), and 30 malignant melanomas (MM). AgNORs in 200 nuclei were scored and the means calculated. Counts were as follows: BN showed a mean of 1.3 AgNORs per nucleus within a range of 1.1-1.6; DN showed a mean of 1.2 within a range of 1.0-1.6; and MM showed a mean of 2.1 within a range of 1.2-4.2. A significant difference existed between counts for MM and those for BN and DN, despite some overlap. There was no statistically significant difference between BN and DN. Although still within the field of research, the AgNOR technique may prove to be of value in helping to differentiate MM from DN, but is unlikely to be of help in separating DN from BN.