Phenotypic relationships of prostatic intraepithelial neoplasia to invasive prostatic carcinoma. Thirty-one snap-frozen human prostate specimens containing examples of benign hyperplasia, prostatic intraepithelial neoplasia (PIN), and invasive carcinoma were analyzed using a panel of 24 antibodies and one lectin. Twenty-seven additional routinely processed radical prostatectomy specimens were studied using selected probes known to work on formalin-fixed paraffin-embedded material. Three probes, anticytokeratin KA4, anti-vimentin V9, and the lectin from Ulex europaeus (UEA-1), demonstrated phenotypic similarities between PIN and invasive carcinoma. Whereas the luminal cells of normal or hyperplastic prostatic epithelium are minimally reactive with KA4 (4%) or UEA-1 (0%) and strongly reactive with anti-vimentin (91%), both the PIN and invasive carcinoma are reactive with KA4 (89% and 93%, respectively) and UEA-1 (96% and 93%, respectively) and minimally reactive with anti-vimentin (15% and 0%, respectively). The increased KA4 staining was shown to be in part due to detection of cytokeratin 19, by using cytokeratin-19-specific antibodies, 4.62 and LP2K. The reasons for the increased expression of this cytokeratin and the decreased expression of vimentin are unclear but seem to indicate a phenotypic relationship between the PIN lesions and invasive carcinoma. 