Objective: This study was conducted to gain a better understanding of the underlying cellular events involved in the development of prostatic intraepithelial neoplasia (PIN) and to clarify the relationship of PIN to invasive prostatic adenocarcinoma (PCa). Method: This article reviews previous studies from our laboratory and others of biomarker expression in PIN and PCa. Results: The development of PIN is characterized by increased expression of several biomarkers which may influence the proliferative potential of the dysplastic cells. Increased expression of the growth factor receptors P185(erbB-2), p180(erbB-3), as well as the product of the c-met proto-oncogene is frequently detected in the dysplastic luminal cells as well as malignant cells of the prostate. Likewise, the expression of the nm-23H1 gene product is strongly expressed in dysplastic and malignant cells. Increased proliferative potential of the dysplastic cells is directly reflected by increased expression of PCNA. In contrast to the enhanced expression of the biomarkers associated with proliferation, decreased expression of prostate-specific antigen (PSA), prostatic acid phosphatase (PAP) and Leu 7 by dysplastic luminal cells is indicative of an impairment of the process of cellular differentiation. Aberrant glycosylation as well as the inappropriate expression of glycosylated tumor antigens is demonstrated by enhanced binding of the lectin Ulex europaeus and increased expression of tumor-associated glycoprotein 72 (TAG-72) and the Lewis Y antigen in dysplastic and malignant cells. Finally, enhanced expression of proteolytic enzymes such as cathepsin D and the 72-kD form of collagenase IV by dysplastic cells may represent an integral event in the development of invasive PCa. Conclusion: The studies described in this review clearly demonstrate phenotypic similarities of PIN to invasive PCa and furthermore support the concept that PIN represents a preinvasive lesion.