Prostate Cancer Detection Methods

Prostate Cancer Detection Methods

Screening for prostate cancer can detect the disease when no symptoms are present and can help catch it at an early stage when treatment is thought to be more effective and potentially has fewer side effects. As noted previously, the most widely used screening tests for prostate cancer include the digital rectal examination (DRE) and the prostate specific antigen (PSA) test. The DRE and PSA test cannot confirm whether or not cancer is present, but they can suggest the need for further tests. If the DRE and PSA test suggest the presence of prostate cancer, a transrectal ultrasound (TRUS)–guided biopsy is typically recommended.

Digital Rectal Exam (DRE)
During a digital rectal examination the physician feels the back portion of the prostate for size and any irregular or abnormally firm areas. For this test, the physician inserts a gloved and lubricated finger into the rectum.

Prostate Specific Antigen Test (PSA)
PSA is a substance produced by cells from the prostate. Under normal circumstances, PSA is secreted by the prostate into semen to help with reproduction by preventing the coagulation of semen. However, small amounts of PSA naturally leak out into the bloodstream as well. When prostate cancer is present, the prostate ducts that normally secrete PSA into the urethra get clogged and more PSA leaks out of the prostate into the bloodstream.

During the PSA test, a small amount of blood is drawn from the arm, and PSA levels are measured. PSA blood test results are reported as nanograms per milliliter (ng/ml). Results under 4 ng/ml are usually considered normal (however, some experts have recently argued that 2.5 ng/ml should be established as the upper limit of “normal”). Results over 10 ng/ml are high, and results between 4 and 10 are considered intermediate. The higher the PSA level, the more likely a patient has prostate cancer. However, many factors can affect PSA levels, and for some people, a high PSA level is normal and does not indicate a problem. The test can also be influenced by certain medical procedures and the presence of an infection. It may be abnormally high (though usually not as high) in men with non-cancerous enlargement of the prostate (benign prostatic hyperplasia or BPH). Also, some medications and herbal preparations can cause an inaccurate reading of blood PSA levels.

Some helpful hints for obtaining a maximally accurate PSA test include: (1) Don’t ejaculate for 2 days prior to having a PSA test as this can raise PSA levels, and (2) tell your doctor if you are taking Proscar, Avodart or Propecia. These drugs, used to treat BPH and baldness, will likely lower your PSA levels. Also, (3) be sure that the DRE is performed after drawing blood for the PSA test, as the DRE can artificially raise PSA levels. Herbal supplements can also affect PSA levels. Be sure to tell your physician about any supplements that you are taking before the PSA test.

Percent Free PSA
This test measures how much PSA circulates freely in the blood and how much is bound with other proteins. The more free PSA that is present the better (or the more likely a man is to be “free” of cancer). So, if a man has an elevated total PSA, but most of it is “free PSA,” then it is most likely coming from BPH rather than cancer. Conversely if most of the total PSA is coming from PSA that is bound to proteins, it is more likely that the patient will have cancer. In one study, researchers used a free-PSA cutoff range of 19% in men with total PSA levels between 3 and 4 and detected 90% of all cancers. In another study of men with total PSA levels between 4 and 10, biopsies were performed only in men with free PSA of less than 25% of the total PSA. They detected 95% of the cancers and reduced unnecessary biopsies by 20%.

PSA Density (PSAD)
PSA density is the value of the PSA divided by the size of the prostate, which can be determined by a transrectal ultrasound (TRUS). The likelihood of prostate cancer is increased when the PSAD value is high. In other words, if you have a relatively small prostate that is producing large amounts of PSA, there is a greater likelihood that cancer is present. If the prostate is large relative to the PSA score, there is a greater chance that BPH is to blame.

PSA Velocity
Calculating the PSA velocity tracks changes in the PSA blood level over time - for example, how quickly the PSA level rises over the course of several months. PSA velocity may aid the interpretation of borderline PSA results by measuring whether the PSA levels are increasing over a short period of time. The test is used as a tool to keep track of how PSA levels change, but it is not used to diagnose prostate cancer. If PSA increases dramatically in a short period, it may be one indicator that prostate cancer has progressed.

Transrectal Ultrasound (TRUS)
The Transrectal Ultrasound (TRUS) procedure uses sound waves to create an image of the prostate to help guide the biopsy needles. It has been shown that TRUS alone is of limited, if any, value in the diagnosis of prostate cancer and is now used primarily to guide biopsy needles.

Prostate Biopsy
The DRE and PSA tests cannot diagnose prostate cancer; they merely indicate that further testing is needed. Abnormal findings in either the DRE or PSA may indicate the need for a biopsy. During a biopsy, a TRUS is used to view and guide a needle (or multiple needles) into the prostate to take small samples of tissue. Typically, a prostate cancer biopsy employs a multi-needle device that is able to take six or more tissue samples simultaneously from different parts of the prostate to be sure that cancerous tissue is not missed. This procedure is typically performed using local anesthesia.

Some physicians will take 12 or more tissue samples or “cores” during a biopsy. These tissues are then examined for the presence of cancer. This generates a value known as a Gleason Grade (Click here for more information), which is used to diagnose the grade of the disease or how far it may have progressed.

A biopsy is the only way to confirm or diagnose the presence of prostate cancer. The biopsy procedure may cause some discomfort or pain, but the procedure is short, and it can usually be performed without an overnight hospital stay, on an outpatient basis. After a biopsy, blood may be present in the urine, semen and/or bowel movements, but these symptoms generally disappear after a few weeks.

Some men worry that a biopsy might help spread the cancer cells either throughout the prostate or beyond. There is no evidence that cancer biopsies of any kind result in the spread of cancer.

While biopsies are the most accurate means of detecting the presence of cancer in the prostate, it is possible to miss a significant cancer during a biopsy – or receive a false-negative result. Prostate cancer does not typically grow as one single tumor or grouping of cancer cells. Rather, prostate cancer is usually comprised of many different small tumors or cancer cell groupings in different areas of the prostate. For this reason, the exact location of these various small tumors can be difficult to pinpoint with the biopsy needles. The needles are directed to the locations in the prostate that are most likely to contain prostate cancer. However, the biopsy is only a sampling of tissue from various parts of the prostate. If very strong signs of cancer were present prior to the biopsy, such as a prostate lump felt during the DRE, a very high PSA and/or an elevated PSA with a very low percentage of free PSA, but no cancer was found, the patient should discuss repeating the biopsy with his physician.

(from http://www.prostatecancerfoundation.org)