Prostate cancer is a common cancer among males. There are often no symptoms in the early stages, but screening can help people detect prostate cancer while it is still treatable.
Screening tests look for markers. These are unusual levels of proteins and other substances that can indicate that cancer is present.
Current tests include the prostate-specific antigen (PSA) blood test, which tests for high levels of the PSA protein. However, this can sometimes produce a false-positive result, suggesting that prostate cancer is present when it is not. This may lead to anxiety and unnecessary further testing.
Prostate cancer is the second most common cancer among males in the United States, after skin cancer. In fact, according to the American Cancer Society (ACS), 1 in 9 men will receive a diagnosis of prostate cancer during their lifetime.
Effective treatment is available in most cases. Those who receive a diagnosis in the early stages are almost certain to survive for at least another 5 years.
For this reason, scientists have been looking for other reliable markers to screen for. Testing for a substance called prostate cancer antigen 3 (PCA3) may be one solution.
Trade names for this test include Progensa and GenProbe.
The ACS advise that males with an average risk of prostate cancer should start screening from the age of 50. Those with a higher risk should start earlier.
Currently, the standard way of screening for prostate cancer is with the PSA blood test. Experts do not recommend the digital rectal exam (DRE).
High PSA levels can indicate prostate cancer, but they can also indicate other conditions. This is because both cancerous and noncancerous cells in the prostate gland can produce PSA.
Other factors that can affect PSA levels include:
- age, as higher levels are more common among older adults
- having a large prostate gland
- having an enlarged prostate, or benign prostatic hyperplasia
- inflammation or infection, such as prostatitis or a urinary tract infection
- stimulation of the prostate, which can happen during a DRE
- medications, some of which increase PSA levels and some of which reduce them
If a test shows that PSA levels are high, the doctor will likely recommend a biopsy to test for cancer. This is an invasive procedure, and it can lead to anxiety, discomfort, and possibly complications.
In a 2018 statement of recommendations, the U.S. Preventive Services Task Force (USPSTF) noted that routine PSA testing may overdiagnose prostate cancer by 20–50%. They expressed concerns about the physical and emotional risks of receiving a false-positive result, which can lead to unnecessary biopsies and even treatment.
The statement concluded that although PSA testing may save lives, the choice to attend screening should be a personal one. The authors urge males ages 55–69 years to make the decision after talking to their doctor.
The USPSTF do not recommend PSA screening for men aged 70 or above.
Also, experts disagree on what “normal” PSA levels should be. One 2004 study, for example, found that doctors had diagnosed some high grade prostate cancers in males with normal PSA levels.
Finally, the studies that researchers used to work out the typical PSA range mostly involved white males.
According to the National Cancer Institute (NCI), “There is no clear consensus regarding the optimal PSA threshold for recommending a prostate biopsy for men of any racial or ethnic group.”
A PCA3 test may help a doctor decide whether or not to perform a biopsy on a person with high PSA levels.
What happens during a prostate biopsy? Find out here.
The PCA3 test may be one way to obtain more accurate results when screening for prostate cancer.
PCA3 is a gene that exists in all prostate gland cells. It causes these cells to make small amounts of certain proteins. It is also present in urine.
Prostate cells that are cancerous can make 60–100 times more of this protein than noncancerous cells. When this happens, the extra proteins will eventually leak into the urine.
If tests detect this protein in the urine, it can signal that prostate cancer is present.
Initial studies showed that these proteins were present in around 95% of prostate cancer samples. They were also more likely to be present in high levels in cancerous tissue, compared with benign tissue. In other words, a person who does not have cancer is unlikely to have significant amounts of this protein.
The PCA3 test may therefore be helpful when PSA test results are abnormal.
Examples of such results include:
- having a high PSA level but a negative biopsy
- having cancer despite also having low PSA levels
- having a high PSA level as well as prostatitis
The advantage of the PCA3 test is that noncancerous conditions do not affect PCA3 levels. High levels of PSA may indicate cancer, but they can also result from other factors — ranging from older age to an infection.
The authors of a 2015 study involving 407 men concluded that the PCA3 test could be useful as both a diagnostic tool and in working out the prognosis for prostate cancer. They found that it was more likely to indicate prostate cancer than two types of PSA test.
In addition, people with more aggressive tumors tended to have a higher PCA3 score.
The Gleason score is one way of describing the grade of cancer cells. Learn more here.
No special preparations are necessary before undergoing a PCA3 test, but knowing what to expect can help put a person at ease.
If a doctor offers a PCA3 test, people should check whether their insurance covers it before going ahead.
A PCA3 test has two parts:
Rectal examination: First, a health professional will carry out a rectal examination. As well as feeling for lumps or other changes, they may also massage the prostate. This will encourage more PCA3 proteins to enter the urine before the next part of the test.
Urine test: Immediately after this, the person will provide a urine sample that the doctor will send to a laboratory for analysis.
The results should be available within a few days.
After receiving the results of a PCA3 test, a discussion about the next steps will take place.
Depending on the results, the doctor may recommend:
- continuing with routine screening, if the result is negative
- taking a “watch and wait” approach, with testing at intervals, to see if the results change
- further testing, to confirm if cancer cells are present
Additional testing may include:
- a biopsy, which means removing a few cells for testing in a laboratory
- a transrectal ultrasound of the prostate cell
- an MRI scan of the prostate gland, to look for growths
The PCA3 test is not currently a standard test for prostate cancer. Instead, a urologist might order it when an initial PSA test result is abnormal.
Not everyone will have a PCA3 test, but the Food and Drug Administration (FDA) have approved its use in certain cases.
For example, a doctor may use it to help decide whether or not to recommend repeat biopsies for males aged over 50 or who have had a previous negative biopsy.
They may also use it to help confirm whether or not prostate cancer is present in males who have a negative biopsy but who continue to have high PSA levels.
The PCA3 test remains a relatively new way of screening for prostate cancer, and its use is not yet widespread. However, it may hold promise for the future.
The NCI note that researchers are looking into ways of combining the PCA3 test with other tests for a more accurate result during screening.
What is the outlook for prostate cancer? Learn more here.