Nucleolar organizer regions (AgNOR) and Ki-67 immunoreactivity in cutaneous melanocytic lesions.

A stepwise schema for the developmental biology of malignant melanomas has been proposed. In this study, two properties associated with malignant transformation--AgNOR production and Ki-67 immunoreactivity--were tested on a series of lesions representative of this model. Fourteen ordinary nevi (N), seven dysplastic nevi (DN), 12 radial growth phase melanomas (RGPM), and eight vertical growth phase melanomas (VGPM) were stained for AgNORs; Ki-67 immunoreactivity was determined in paraffin sections after antigen retrieval. AgNORs averaged 2.1 in N, 3.8 in DN, 5.4 in RGPM, and 7.3 in VGPM (p < 0.001 between all groups). Ki-67 immunoreactivity averaged < 1 in nevi, 1.6 in dysplastic nevi, 23.3 in RGPM, and 20.1 in VGPM. No difference was observed between N and DN, and RGPM/VGPM had higher Ki-67 indices than N/DN (p < 0.01). Stepwise increases in cellular AgNORs parallel the melanocytic progression model and thereby corroborate the intermediate nature of the dysplastic nevus. The order of magnitude increase in Ki-67 immunoreactivity observed in RGP and VGP melanomas compared with N and DN likely reflects the onset of loss of cell cycle control in these lesions.