[Proper use of prostate specific antigen].
Prostate specific antigen (PSA) has become the best marker for prostatic carcinoma. PSA is secreted by the glandular cells of prostatic epithelium and is specific for any normal, hyperplasic and tumoral prostatic tissue. PSA is excreted in blood that render its dosage accessible for clinical purpose. Two different tests are now used: Tandem test R is a radioimmunological test (N1:0-4 ng/mL), and Pros check test uses an immunoenzymatic method and is considered to be more sensitive (N1: < 2.5 ng/mL). PSA increases of 35 ng/mL for every other gram of hyperplastic prostatic tissue and of 3.5 ng/mL by gram of prostatic cancer. This test allows detection of prostate carcinoma with a positive predictive value of 49% when PSA > 4 ng/mL and 75% when PSA > 10 ng/mL. However, only biopsies will confirm the diagnostic of prostate cancer. For the patients with an increased PSA and no cancer founded by random biopsies, an increase of PSA level in the next year suggests prostate carcinoma. When the diagnostic of prostate cancer has been made, a PSA < 15 ng/mL suggests a low stage carcinoma (B1 or B2). When PSA > 75 ng/mL, there is a high probability that this cancer is node positive. Between this values, PSA cannot make the difference between stage B, C or D. The more sensitive test (Pros check) must give undetectable level after radical prostatectomy. For high stage lesion treated by hormonotherapy, or chemotherapy or radiation therapy, PSA is a good indicator of response to therapy and recurrence after therapy.