Prostate cancer exceeds lung cancer as the most commonly diagnosed cancer in the United States and it is the second leading cause of cancer death in men. Despite the use of PSA, novel markers are needed which are able to identify prostate cancer early in a specific fashion. Focusing on the hallmark of the cancer cell, changes in nuclear and cellular structure, we have identified several nuclear matrix proteins that are specific for prostate cancer. One of these proteins, EPCA is localized throughout the prostate in individuals with prostate cancer but is not found in the prostates of men without the disease. We have generated antibody reagents against EPCA and demonstrate that it is able to detect the protein in the negative biopsies of men who an average of two years later are diagnosed with prostate cancer. In addition, we have been able to detect the protein in the serum of individuals with metastatic prostate cancer. We therefore hypothesize that EPCA may serve as a biomarker for prostate cancer and that it has a potential role in prostate cancer pathobiology. In this Phase I application we propose to generate sufficient data to move this discovery toward commercial application. Specifically, we will (1) evaluate the efficacy of EPCA as a biomarker for prostate cancer in detecting individuals with "negative" biopsies; (2) determine the tissue specificity of EPCA by staining a spectrum of normal and tumor tissues for ECPA expression; and (3) develop a serum-based assay to detect EPCA in the serum of individuals with prostate cancer. Our studies in this application will focus on assay validation, determination of specificity, as well as expansion of our data set. These studies will provide the necessary data to move forward with the Phase II commercialization of this product which in turn will have a significant impact on men that are being biopsied for prostate cancer.