Screening refers to testing to find a disease such as cancer in people who do not have symptoms of that disease. For some types of cancer, screening can help find cancers in an early stage when they are more easily cured.
Prostate cancer can often be found early by testing the amount of prostate-specific antigen (PSA) in the blood. Another way to find prostate cancer is the digital rectal exam (DRE), in which your doctor puts a gloved finger into the rectum to feel the prostate gland. These 2 tests are described below in more detail. If the results of either one of these tests are abnormal, further testing is needed to see if there is a cancer.
If prostate cancer is found during screening with the PSA test or DRE, your cancer will likely be at an early, more treatable stage than if no screening were done.
Since the use of early detection tests for prostate cancer became fairly common (about 1990), the prostate cancer death rate has dropped. But it isn't yet clear if this drop is a direct result of screening or caused by something else, like improvements in treatment.
There are limits to the prostate cancer screening tests used today. Neither the PSA test nor the DRE is 100% accurate. These tests can have abnormal results even when cancer is not present (known as false positive results). In addition, normal results can occur even when cancer is present (known as false negative results). Unclear test results can cause confusion and anxiety. False positive results can lead some men to undergo a prostate biopsy (with small risks of pain, infection, and bleeding) when cancer is not present. And false negative results may give some men a false sense of security even though they actually have cancer.
There is no question that the PSA test can help spot many prostate cancers early, but another important issue is that it can't tell how dangerous the cancer is. Finding and treating all prostate cancers early may seem like a no-brainer. But some prostate cancers grow so slowly that they would likely never cause problems. Because of an elevated PSA level, some men may be diagnosed with a prostate cancer that they would have never even known about at all. It would never have lead to their death or even caused any symptoms. But they may still be treated with either surgery or radiation, either because the doctor can't be sure how aggressive (fast growing and fast spreading) the cancer might be, or because the men are uncomfortable not having any treatment. Treatments like surgery and radiation can have side effects that may seriously affect a man's quality of life. These treatments can lead to urinary, bowel, and/or sexual problems. In some men these problems may be minimal and/or short-term, but for others these problems can be severe and long-lasting (or even permanent). Doctors and patients are still struggling to decide who should receive treatment and who might be able to be followed without being treated right away (an approach called watchful waiting or active surveillance). Even when patients are not treated right away, they still need regular blood tests and prostate biopsies to determine the need for future treatment. These tests are linked with risks of anxiety, pain, infection, and bleeding.
Studies are being done to try to figure out if early detection tests for prostate cancer in large groups of men will lower the prostate cancer death rate. The most recent results from 2 large studies were conflicting, and didn't offer clear answers.
Early results from a study done in the United States found that annual screening with PSA and DRE detected more prostate cancers, but it did not lower the death rate from prostate cancer. A European study did find a lower risk of death from prostate cancer with PSA screening (done about once every 4 years), but the researchers estimated that about 1,400 men would need to be screened (and 48 treated) in order to prevent one death from prostate cancer. Neither of these studies has shown that PSA screening helps men live longer (lowered the overall death rate).
Recently, early results of a Swedish study of prostate cancer screening were published. One group of men was offered PSA testing every other year, with follow-up tests including biopsy if the PSA was over a certain level. This study did not test elderly men - those over 71 years old were not tested. Cancer and death rates in the group offered testing were compared to a group of men who were not offered testing. After 15 years, the group that was offered testing had lower risk of death from prostate cancer, but the overall death rate was the same in both groups.
Prostate cancer tends to be a slow growing cancer, so the effects of screening in these studies may become clearer in the coming years. Both of these studies are being continued to see if longer follow-up will give clearer results.
At this time, the American Cancer Society (ACS) recommends that men thinking about prostate cancer screening should make informed decisions based on available information, discussion with their doctor, and their own views on the benefits and side effects of screening and treatment (see below).
Until more information is available, you and your doctor can decide whether you should have tests to screen for prostate cancer. There are many factors to take into account, including your age and health. If you are young and develop prostate cancer, it may shorten your life if it is not caught early. Screening men who are older or in poor health in order to find early prostate cancer is less likely to help them live longer. This is because most prostate cancers are slow-growing and men who are older or sicker are likely to die from other causes before their prostate cancer grows enough to cause problems.
American Cancer Society recommendations for the early detection of prostate cancer
The American Cancer Society recommends that men have a chance to make an informed decision with their health care provider about whether to be screened for prostate cancer. The decision should be made after getting information about the uncertainties, risks, and potential benefits of prostate cancer screening. Men should not be screened unless they have received this information.
The discussion about screening should take place at age 50 for men who are at average risk of prostate cancer and are expected to live at least 10 more years.
This discussion should take place starting at age 45 for men at high risk of developing prostate cancer. This includes African American men and men who have a first-degree relative (father, brother, or son) diagnosed with prostate cancer at an early age (younger than age 65).
This discussion should take place at age 40 for men at even higher risk (those with several first-degree relatives who had prostate cancer at an early age).
After this discussion, those men who want to be screened should be tested with the prostate specific antigen (PSA) blood test. The digital rectal exam (DRE) may also be done as a part of screening.
If, after this discussion, a man is unable to decide if testing is right for him, the screening decision can be made by the health care provider, who should take into account the patient’s general health preferences and values.
Men who choose to be tested who have a PSA of less than 2.5 ng/ml, may only need to be retested every 2 years.
Screening should be done yearly for men whose PSA level is 2.5 ng/ml or higher.
Because prostate cancer grows slowly, those men without symptoms of prostate cancer who do not have a 10-year life expectancy should not be offered testing since they are not likely to benefit. Overall health status, and not age alone, is important when making decisions about screening.
Even after a decision about testing has been made, the discussion about the pros and cons of testing should be repeated as new information about the benefits and risks of testing becomes available. Further discussions are also needed to take into account changes in the patient's health, values, and preferences.
Prostate-specific antigen (PSA) blood test
Prostate-specific antigen (PSA) is a substance made by cells in the prostate gland (it is made by normal cells and cancer cells). PSA is mostly found in semen, but a small amount is also found in the blood. Most healthy men have levels under 4 nanograms per milliliter (ng/mL) of blood. The chance of having prostate cancer goes up as the PSA level goes up.
When prostate cancer develops, the PSA level usually goes above 4. Still, a level below 4 does not mean that cancer isn't present -- about 15% of men with a PSA below 4 will have prostate cancer on biopsy. Men with a PSA level in the borderline range between 4 and 10, have about a 1 in 4 chance of having prostate cancer. If the PSA is more than 10, the chance of having prostate cancer is over 50%.
The PSA level can also be increased by things other than prostate cancer, such as:
- An enlarged prostate, such as with benign prostatic hyperplasia (BPH), a non-cancerous enlargement of the prostate that many men get as they grow older
- Age: PSA levels will also normally go up slowly as you get older, even if you have no prostate abnormality.
- Infection or inflammation of the prostate gland (prostatitis)
- Ejaculation can cause the PSA to go up for a short time, and then go down again. This is why some doctors will suggest that men abstain from ejaculation for 2 days before testing.
- Riding a bicycle
- Certain urologic procedures
Some things cause PSA levels to go down (even when cancer is present), including:
- Certain medicines used to treat BPH or urinary symptoms, such as finasteride (Proscar or Propecia) or dutasteride (Avodart). You should tell your doctor if you are taking these medicines, because they will lower PSA levels and require the doctor to adjust the reading.
- Some herbal mixtures that are sold as dietary supplements may also mask a high PSA level. This is why it is important to let your doctor know if you are taking any type of supplement, even ones that are not necessarily meant for prostate health. Saw palmetto (an herb used by some men to treat BPH) does not seem to interfere with the measurement of PSA.
- Some steroids may also change PSA levels
- Obesity: Obese men tend to have lower PSA levels
- Aspirin: Men taking aspirin regularly tend to have lower PSA levels. This effect is most pronounced in non-smokers.
If your PSA level is high, your doctor may advise a prostate biopsy to find out if you have cancer (see the section, “How is prostate cancer diagnosed?”). Some doctors may consider using newer types of PSA tests (discussed below) to help determine if you need a prostate biopsy, but not all doctors agree on how to use these other PSA tests. If your PSA test result is not normal, ask your doctor to discuss your cancer risk and your need for further tests.
Percent-free PSA
PSA occurs in 2 major forms in the blood. One form is attached to blood proteins while the other circulates free (unattached). The percent-free PSA (fPSA) is the ratio of how much PSA circulates free compared to the total PSA level. The percentage of free PSA is lower in men who have prostate cancer than in men who do not.
This test is sometimes used to help decide if you should have a prostate biopsy if your PSA results are in the borderline range (between 4 and 10). A lower percent-free PSA means that your likelihood of having prostate cancer is higher and you should probably have a biopsy. Many doctors recommend biopsies for men whose percent-free PSA is 10% or less, and advise that men consider a biopsy if it is between 10% and 25%. Using these cutoffs detects most cancers while helping some men to avoid unnecessary prostate biopsies. This test is widely used, but not all doctors agree that 25% is the best cutoff point to decide on a biopsy, and the cutoff may change depending on PSA level.
A newer test, known as complexed PSA, measures the amount of PSA that is attached to other proteins. This test is described in more detail in the section, "What's new in prostate cancer research and treatment?"
PSA velocity
The PSA velocity is not a separate test. It is a measure of how fast the PSA rises over time. Normally, PSA levels go up slowly with age. Experts noticed that these levels can go up faster when cancer is present. When this issue was looked at further, though, studies showed that the PSA velocity was not more helpful than the PSA itself in finding prostate cancer. For this reason, the most recent ACS guideline on early detection of prostate cancer does not recommend using the PSA velocity.
PSA density
PSA levels are higher in men with larger prostate glands. The PSA density (PSAD) is sometimes used for men with large prostate glands to try to adjust for this. The doctor measures the volume (size) of the prostate gland with transrectal ultrasound (discussed below) and divides the PSA number by the prostate volume. A higher PSA density (PSAD) indicates greater likelihood of cancer. PSA density has not been shown to be that useful. The percent-free PSA test has so far been shown to be more accurate.
Age-specific PSA ranges
PSA levels are normally higher in older men than in younger men, even when there is no cancer. A PSA result within the borderline range might be very worrisome in a 50-year-old man but cause less concern in an 80-year-old man. For this reason, some doctors have suggested comparing PSA results with results from other men of the same age.
But because the usefulness of age-specific PSA ranges is not well proven, most doctors and professional organizations (as well as the makers of the PSA tests) do not recommend their use at this time.
Using the PSA blood test after prostate cancer diagnosis
The PSA test is used mainly to detect prostate cancer early, but it is useful in other situations:
- In men diagnosed with prostate cancer, the PSA test can be used together with clinical exam results and tumor grade (from the biopsy) to help decide if further tests (such as CT scans or bone scans) are needed.
- It can help tell whether your cancer is still confined to the prostate gland. If your PSA level is very high, your cancer has likely spread beyond the prostate. This may affect your treatment options, since some forms of therapy (such as surgery and radiation) are not likely to be helpful if the cancer has spread to the lymph nodes, bones, or other organs.
- After surgery or radiation treatment, the PSA level can be watched to help determine if the treatment was successful. PSA levels normally fall to very low levels if the treatment removed or destroyed all of the prostate cells. A rising PSA level (especially after surgery) likely means that prostate cancer cells are present and your cancer has come back. Having a detectable PSA level does not always mean that you still have cancer. If you have a low PSA level that is not rising, it could mean that you just have some benign prostate cells still in your body.
- If you choose a "watchful waiting" approach to treatment, the PSA level can be used to help decide whether the cancer is growing and if active treatment should be considered.
- During hormonal therapy or chemotherapy, the PSA level can help indicate how well the treatment is working or when it may be time to try a different form of treatment.
If prostate cancer has come back (recurred) after treatment, or if it has spread outside of the prostate (metastatic disease), the actual PSA number is probably not as important as whether it changes, and how quickly it changes. The PSA number does not predict whether or not a person will have symptoms or how long he will live. Many people have very high PSA values and feel just fine. Other people have low values and have symptoms.
Digital rectal exam (DRE)
For a digital rectal exam (DRE), a doctor inserts a gloved, lubricated finger into the rectum to feel for any bumps or hard areas on the prostate that might be cancer. The prostate gland is found just in front of the rectum, and most cancers begin in the back part of the gland, which can be felt during a rectal exam. This exam is uncomfortable, but it isn't painful and only takes a short time. It is more uncomfortable in men who have hemorrhoids.
DRE is less effective than the PSA blood test in finding prostate cancer, but it can sometimes find cancers in men with normal PSA levels. For this reason, it may be included as a part of prostate cancer screening.
The DRE can also be used once a man is known to have prostate cancer to try to determine if it may have spread to nearby tissues and to detect cancer that has come back after treatment.
Transrectal ultrasound (TRUS)
Transrectal ultrasound (TRUS) uses sound waves to make an image of the prostate on a video screen. For this test, a small probe that gives off sound waves is placed into the rectum. The sound waves enter the prostate and create echoes that are picked up by the probe. A computer turns the pattern of echoes into a black and white image of the prostate.
The procedure often takes less than ten minutes and is done in a doctor's office or outpatient clinic. You will feel some pressure when the TRUS probe is placed in your rectum, but it is usually not painful. The area may be numbed before the procedure.
TRUS is not used as a screening test for prostate cancer because it doesn't often show early cancer. Instead, it is most commonly used during a prostate biopsy (described in the next section). TRUS is used to guide the biopsy needles into the right area of the prostate.
TRUS is useful in other situations as well. It can be used to measure the size of the prostate gland, which can help determine the PSA density and may also affect which treatment options a man has. It is also used as a guide during some forms of treatment such as cryosurgery (discussed in the Treatment section).
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