PSA – A Marker for Prostate Cancer
Prostate Specific Antigen (PSA), a tumor marker for prostate cancer is fairly precise in detecting prostate cancer.
This antigen is found in low levels in all male; the normal value is 0-4 ng /ml. PSA can be detected in the epithelium or in the secretions of a normal prostate but is not found in other tissues.
PSA is specific to the prostate and is not cancer cancer-specific. Therefore elevated levels of this marker is seen in an array of conditions such as prostatitis (inflammation of the prostate) and benign hypertrophy of the prostate (enlargement of the prostate) besides prostate cancer. Interestingly PSA was first used in Forensic Medicine to identify presence of semen on clothes of women who were rape victims.
In the blood PSA exists in the following forms:
- Free PSA: Exists freely in the blood and is not bound to other proteins
- Bound PSA: adhered to another protein, which could be α-Antichymotrypsin or α-2 macroglobulin
The standard tests for PSA levels detects free PSA and the PSA bound to α-Antichymotrypsin. Research has established that individuals with prostate cancer has lower levels of free PSA compared to disease-free individuals.
It has been recommended that the ratio of free PSA to the total PSA can help to differentiate between malignant or a benign disease in the prostate. However there is no consensus regarding this method. There is doubt regarding the correlation of this ratio value to the presence or absence of cancer.
PSA is fairly precise in detecting cancer of the prostate and in assessing the stage and tumor volume. A high PSA value alerts one to the need for further followup. It is very useful in analyzing cancer recurrence and treatment response .
PSA is not cancer-specific. Prostatitis (inflammation of the prostate) and benign hypertrophy of the prostate (enlargement of the prostate) besides prostate cancer. Interestingly PSA was first used in Forensic Medicine to identify presence of semen on clothes of women who were rape victims.
Age and race are also known to influence the PSA levels. African Americans are found to have elevated PSA levels in comparison to Asian men.
