A tumor marker is a substance produced by a tumor, possibly measurable in body fluids, which is useful for diagnosis and management of cancer. A tumor marker was described 150 years ago when Bence-Jones noted the presence of abnormal proteins in the urine of patients with what now is known as a multiple myeloma.<sup>30 Sell S. Cancer markers  Baltimore: Williams & Wilkins (1991).  225

Cliccare qui per andare alla sezione Riferimenti</sup> Urologists are particularly familiar with tumor markers using alpha fetoprotein, beta-human chorionic gonadotropin, and lactate dehydrogenase for testes cancer and prostatic acid phosphatase (PAP) and more recently prostate-specific antigen (PSA) for prostate cancer. Other well accepted markers in oncology include carcinoma embryonic antigen for colon cancer and CA-125 for ovarian cancer. Interestingly, PSA is emerging as probably the best marker in oncology and clearly has had a profound impact on all aspects of prostate cancer care.<sup>22 Partin A.W., Oesterling J.E. The clinical usefulness of prostate specific antigen: Update 1994 J Urol 1994 ;  152 : 1358

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A tumor marker may be useful for diagnosis, early detection, staging, prognosis, and follow-up after treatment. No currently available marker performs ideally in all settings; performance characteristics depend on specific aspects of each cancer such as prevalence, tumor heterogeneity, and response to therapy. Technical advances in molecular biology are opening new strategies for detection of tumor markers providing a field with rapid evolution. Acknowledging that the perfect tumor marker does not exist, it is valuable to examine the characteristics of what might be an ideal tumor marker for prostate cancer and how well PSA performs in this light.