Aspects and Applications of Tumor Markers

Researchers have developed a multitude of new markers, and it is considered that these new markers will have greater clinical utility than markers of the past. These research studies show that we can expect these markers to bring about a change in therapy of patients or quality of life. As these new markers become available for some of the most common forms of cancer, the clinical laboratories will play an important role in diagnosing and treating malignancies and standardizing marker tests to achieve comparable results that contribute to the patients medical care and quality of life. 

Increased diagnosis of prostate cancer is attributed in part to the increased utilization of PSA testing. In fact, the American Cancer Society (ACS) now recommends measurement of PSA in addition to digital rectal examinations (DREs) in men over 50 years of age. Early detection of clinically localized prostate cancer can potentially result in a cure with radical prostatectomy or other treatments. PSA tests are used to monitor therapeutic efficacy and detect recurrent disease in patients with prostate cancer. 

PSA determination can be used to investigate the necessity for a prostate biopsy. PSA is considered a useful analyte in the diagnosis and management of prostate cancer however, increased serum concentrations of PSA are also seen in patients without cancer of the prostate (e.g., patients with bacterial prostatitis or benign 

Patients must be monitored to assess their response to treatment and to detect recurrent diseases. PSA as a specific marker for prostate cancer is most useful in monitoring patients who have been treated with radical prostatectomy, radiation therapy, or endocrine therapy. The concentration of PSA falls to undetectable levels following a radical prostatectomy because all prostate tissue has been removed. Generally, PSA is measured at periodic intervals. In studies, the extent of disease at the time of surgery correlated well with the postoperative PSA concentration. A significant measurable PSA concentration after prostatectomy indicates that residual tumor may be present. PSA concentrations decline gradually after radiation therapy (36). 

It has been reported that PSA exists in multiple isoforms in serum free PSA (30-kDa protease) and complexed PS A (100-kDa complex between PSA and A1 ACT). While the PSA in the prostate is in the free form, when the PSA enters the blood stream, the majority binds to A1 ACT. Recent studies have shown that PSA in serum occurs in two molecular forms, free (f-PSA) and bound both PSAs gave equal detectable signals ( equimolar ). Most of the PSA in serum is complexed with either A1 ACT or A2 MG. Different proportions of free and complex isoforms have been detected in the sera of prostate cancer and BPH patients. The fraction 

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