Nucleolar organizer regions as discriminators for the diagnosis of well-differentiated adenocarcinoma of the prostate.

This study sought to determine whether nucleolar organizer region (NOR) counts might be of diagnostic use specifically in the frequently difficult identification of well-differentiated prostate cancer. Total silver-stained NOR (AgNOR) counts on sections were done in 50 consecutive nuclei from 22 cases of well-differentiated adenocarcinoma composed exclusively of Gleason grades 1 or 2 and in 50 consecutive nuclei in foci of benign glands on the same slide. Malignant nuclei contained a mean of 4.84 AgNORs; benign nuclei, 3.39 AgNORs. This difference was statistically highly significant (P < .0001), but there was considerable overlap of mean AgNOR counts between malignant and benign groups. Thus, to obtain a rule requiring a specificity of greater than 95% using the mean AgNOR count as a definition of malignancy, the maximum sensitivity possible was only 32%. Despite the overlap in mean AgNOR counts, however, in all but one case the mean count for malignant nuclei was greater than that for benign nuclei. This suggests that the diagnostic potential of AgNOR counts might be better realized by a comparison of counts between a suspicious focus and an adjacent focus of benign glands.