PSA & DRE Screening for Prostate Cancer

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 inserts a gloved finger into the rectum to feel the prostate gland. If the results of either one of these tests are abnormal, further testing is needed to see if there is a cancer. If you have routine yearly exams and either one of these test results becomes abnormal, then any cancer you might have has likely been found at an early, more treatable stage.

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). Although PSA is mostly found in semen, 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%.

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.

PSA velocity

The PSA velocity is not a separate test. It is a measure of how fast the PSA rises over time. Even when the total PSA value isn't over 4, a high PSA velocity suggests that cancer may be present and a biopsy should be considered. For example, if your PSA was 1.7 on one test, and then a year later it was 3.8, this rapid rise may be cause for concern.

This can be useful if you are having the PSA test every year. For men whose initial PSA value is less than 4, a PSA velocity of 0.35 (ng/mL) per year or greater (for example, if values went from 2 to 2.4 to 2.8 over the course of 2 years) may be cause for concern. For men whose PSA value is between 4 and 10, a biopsy should be more strongly considered if it goes up faster than 0.75 (ng/mL) per year (for example, if values went from 4 to 4.8 to 5.6 over the course of 2 years). Most doctors believe that PSA levels should be measured on at least 3 occasions over a period of at least 18 months in order to get an accurate 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.

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.

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. This is why the American Cancer Society guidelines recommend that when prostate cancer screening is done, both the DRE and PSA blood test should be used.

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 in 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 takes only a few 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.

TRUS is usually not recommended as a routine test by itself to detect 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.

Signs and symptoms of prostate cancer

Early prostate cancer usually causes no symptoms and is most often found by a PSA test and/or DRE. Some advanced prostate cancers can slow or weaken your urinary stream or make you need to urinate more often. But non-cancerous diseases of the prostate, such as BPH (benign prostatic hyperplasia) cause these symptoms more often.

If the prostate cancer is advanced, you might have blood in your urine (hematuria) or trouble getting an erection (impotence). Advanced prostate cancer commonly spreads to the bones, which can cause pain in the hips, spine, ribs, or other areas. Cancer that has spread to the spine can also press on the spinal nerves, which can result in weakness or numbness in the legs or feet, or even loss of bladder or bowel control.

Other diseases can also cause many of these same symptoms. It is important to tell your doctor if you have any of these problems so that the cause can be found and treated.

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