Prostate-specific antigen and early detection of prostate cancer.

Prostate-specific antigen (PSA) is biochemically a 33-kDa serine protease and is the prototype of tumor marker most useful in investigating basic science and clinical application of prostate cancer. As an immunohistopathological marker, PSA is especially effective in the identification of distant metastatic prostate carcinoma and in the differential diagnosis of poorly differentiated transitional cell carcinomas of the bladder from prostate carcinoma. As a serologic marker, PSA is most useful in staging, monitoring and in early detection of recurrent disease. The greatest value of PSA is as a screening aid along with digital rectal examination for early detection of prostate cancer. PSA-based 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 early nonpalpable prostate cancer. Approximately 85% of the prostate tumors detected through PSA have the clinical features associated with medically important cancer. Further, a majority of the tumors, 70%, are confined to the organ. Although the issues of cost-benefit and increase in ultimate survival rate are still being evaluated in two large-scale randomized national trials, timely and definitive therapies of these potentially lethal tumors can result in high cure rate and improve the quality of patients' life.