Our group has been studying the progressive molecular changes in prostatic epithelium which precede the invasive phenotype. Initial studies revealed similar alterations in cytoskeletal proteins between high grade prostatic intraepithelial neoplasia (PIN) lesions and invasive carcinoma. Specifically we observed an increased expression of certain cytokeratins and decreased expression of vimentin. We also noted a change in glycosylation as detected by Ulex europaeus staining. Using the latter technique we were able to microdissect and isolate nuclei from areas of low and high grade PIN lesions as well as from invasive carcinoma for morphometric analysis. Similarities in nuclear size, chromatin heterogeneity, and nuclear DNA content between low and high grade PIN and invasive carcinoma in carcinomatous specimens were noted. In contrast, these parameters were significantly different in low grade PIN lesions obtained from benign prostatic transurethral resection (TURP) specimens. In addition, DNA histograms revealed similar proliferative indices between high grade PIN and invasive carcinoma, which differed significantly from low grade PIN. Parameters thought to be relative to the invasive phenotype were also examined, such as the members of the metalloproteinase family; although normal luminal cells fail to express detectable levels of these enzymes, invasive carcinoma and even low grade PIN lesions express both the 72 kDa and 92 kDa type IV collagenase. Taken together, these data indicate that the dysplastic cells of PIN lesions and carcinomas are similar in nuclear and genomic features as well as protease expression. Our current working hypothesis is that these cells are already armed with the necessary proteases to invade the basal lamina but in an inactive form. Tumor progression requires an additional event of protease activation.