What is a prostate-specific antigen (PSA)?
Prostate-specific antigen (PSA) is a protein produced by the prostate gland. Blood levels of PSA can be elevated in men with prostate cancer.
For this reason, measurement of PSA in the blood has been used as a screening test for prostate cancer. However, the PSA test was first developed only to monitor men who had a history of prostate cancer. Views about PSA screening and appropriate follow-up have been evolving.
What constitutes an elevated prostate-specific antigen (PSA)?
No single normal level has been established. Historically, a level of 4.0 ng/mL or higher was used to justify a biopsy of the prostate (a sample of prostate tissue) to try and determine if a man has prostate cancer. However, this practice has been changing and other factors are being considered in the decision to perform a prostate biopsy.
Also, the thinking with regard to the management of prostate cancer continues to evolve. Considerations include:
- Aggressiveness of the cancer.
- Volume of cancer detected on biopsy.
- How it will affect a man’s longevity (length of life).
Symptoms and Causes
Does a prostate-specific antigen (PSA) level higher than 4.0 ng/mL mean that I have prostate cancer? Can prostate cancer be ruled out if my level is less than 4.0 ng/mL?
No, prostate cancer has been detected in men with levels less than 4.0 ng/mL. And many men with PSA levels higher than 4.0 ng/mL do not have prostate cancer. There is no PSA level below which the risk of cancer is zero. Two men with the same PSA level may have very different risks of prostate cancer depending on other risk factors.
Factors other than prostate cancer can cause the PSA level to be higher. These include:
- An enlarged prostate and prostate inflammation (prostatitis).
- Urinary tract infection.
- Having had a urinary catheter placed.
Drugs known as 5-alpha reductase blockers (finasteride or dutasteride), which are used at times to treat an enlarged prostate, will lower PSA levels. These factors are important to consider when interpreting the PSA test result.
Generally, higher PSA levels are associated with higher risks of prostate cancer.
Diagnosis and Tests
How should an elevated prostate-specific antigen (PSA) level be interpreted?
A single PSA level by itself may not be the most important factor of cancer risk. Many studies have looked at ways to improve the performance of the test. These studies examine multiple PSA tests and measure the rate at which the PSA level might be increasing, called PSA velocity.
They also look at the ratio of PSA not bound to other proteins, called free PSA, to the total PSA value to add to risk prediction. Other tests divide the level of PSA in the blood by the volume of the transition zone (the area surrounding the urethra) to arrive at a PSA density.
If you have had a PSA screening test, your doctor may want you to have a repeat PSA test if your level is 4.0 ng/mL or above but less than 7.0 ng/ mL. PSA levels can change and may also be affected by various issues such as an enlarged prostate, an inflamed prostate/prostatitis, or urinary retention.
If your doctor recommends a prostate biopsy based on the blood test results, a critical factor will be the interpretation of the biopsy and how it affects your management. If examination of the biopsy tissue detects a large volume of cancer cells, it can signify a more aggressive cancer.
Prostate cancer cells are graded using the Gleason score, which ranges from 2 to 10. The higher the score, the more aggressive the cancer is. Often a score of 6 or less does not require treatment, but a discussion of the biopsy result with the doctor is mandatory.
If a biopsy detects cancer, an imaging test such as a:
- magnetic resonance imaging (MRI),
- computed tomography (CT) scan, or
- radionuclide bone scan
may be done to see if or how far the cancer has spread, called the cancer stage.
The stage also affects the management decision. Cancer that has spread outside of the prostate’s capsule (Stage III or IV) is riskier and more aggressive than one confined to the prostate capsule (Stage I).
Management and Treatment
What does this mean for treatment?
Many prostate cancers are slow-growing and may never threaten a man’s life. Researchers have been looking for ways to identify the aggressive cancers that may need immediate treatment.
Other cancers that are less aggressive may be managed safely by active surveillance or watchful waiting, due to the low risk of long-term harmful effects.
Prostate cancer treatments may cause side effects such as:
- Altered bladder and bowel function.
Therefore, the decision to treat must be discussed in detail with your doctor. At times, it may be best to treat only intermediate- or high-risk cancers. Men with low-risk prostate cancer may not need any treatment and so can avoid these complications if they are managed conservatively with continued monitoring.
Depending on the stage of the cancer, prostate cancer treatments range from monitoring for low-risk disease to:
- Removal of the prostate.
- Radiation therapy.
- Radioactive seed implantation (brachytherapy).
- Freezing (cryotherapy).
- Hormonal treatment.
Each has its own set of side effects. For patients whose cancers develop resistance to hormone therapy, several new agents have received FDA approval over the past few years, including immunotherapy (vaccine) and drugs called abiraterone and enzalutamide.
If you have an elevated PSA and cancer is detected on a biopsy and you choose monitoring instead of treatment, you will continue to have your PSA levels monitored over time. For some older men with a life expectancy of less than 10 years, treatment of their prostate cancer may not extend their lives.
Outlook / Prognosis
What does an elevated prostate-specific antigen (PSA) mean after I’ve had prostate cancer in the past?
Your PSA level will be measured regularly after you have been treated for prostate cancer. Depending on the treatment, an elevated level might mean that the cancer has recurred. More PSA tests may be conducted along with imaging tests and biopsies, for those treated with radiation of cryoablation, to determine if cancer is present and the potential need for more treatment.