Tumour serum markers: clinical and economical aspects

Tumour serum markers represent one of the most interesting challenges in modern oncology. Although know for many years, tumour markers did not receive clinical attention until the '80s. Despite their widespread use, the identification of a tumour marker which is highly sensitive as well as specific for a certain type of cancer, and can be assayed by simple, reproducible and cheap methods, remains elusive. This review deals with the clinical use of the Prostate Specific Antigen (PSA). PSA is biochemically a glycoprotein, is the most valuable tool available for the diagnosis and staging of prostate cancer and one of the most widely used laboratory tests in oncology. Serum PSA can detect twice as many prostate cancers as digital rectal examination can and approximately 70% of these cancers are potentially curable. In assessing the role of PSA in the diagnosis and the monitoring of prostate cancer, new concepts have been developed and are in clinical use today: PSA velocity, free versus complexed PSA, PSA index or PSA density and age-specific reference ranges. By combining serum PSA concentration with histologic grade (Gleason grading system) and clinical stage (TNM staging system), we can predict metastasis to the pelvic lymph nodes. For instance, patients with clinical stage T1a-T2b, Gleason grade 1 or 2 and serum PSA level 17.1 ng/ml or less, have a probability of pelvic lymph nodes involvement approaching zero. So, surgical staging procedures can be avoided in these selected patients. Another group of patients with prostate cancer who can benefit from measuring serum PSA concentration, is the group of newly diagnosed patients, with no skeletal symptoms and a serum PSA concentration less than 10 ng/ml. In this group, the probability of a positive bone scan approaches zero and a staging bone scan is not necessary. From the standpoint of economic analysis, measurement of serum PSA can serve in two ways: Firstly, estimating the savings when PSA is used in a prevention programme in the general population and secondly, calculating the savings in patients with prostate cancer, when PSA is used to complement or substitute other diagnostic or staging procedures.