PROSTATE-SPECIFIC ANTIGEN AND EARLY DETECTION OF PROSTATE-CANCER

Prostate-specific antigen (PSA) is biochemically a 33-kDa serine prote ase and is the prototype of tumor marker most useful in investigating basic science and clinical application of prostate cancer. As an immun ohistopathological marker, PSA is especially effective in the identifi cation of distant metastatic prostate carcinoma and in the differentia l diagnosis of poorly differentiated transitional cell carcinomas of t he bladder from prostate carcinoma. As a serologic marker, PSA is most useful in staging, monitoring and in early detection of recurrent dis ease. The greatest value of PSA is as a screening aid along with digit al rectal examination for early detection of prostate cancer. PSA-base d screening tests have been performed in various regions of the world and have yielded prostate cancer detection rates proportional to that of incidence rates in the countries. Most significantly, PSA detects e arly nonpalpable prostate cancer. Approximately 85% of the prostate tu mors detected through PSA have the clinical features associated with m edically important cancer. Further, a majority of the tumors, 70%, are confined to the organ. Although the issues of cost-benefit and increa se in ultimate survival rate are still being evaluated in two large-sc ale randomized national trials, timely and definitive therapies of the se potentially lethal tumors can result in high cure rate and improve the quality of patients' life.