Prostate Cancer Chapter 7
Screening and Detection
Screening and Testing
Screening is testing someone for a disease when there are no symptoms of the disease present. Screening tests are widely used by clinicians as part of periodic health examinations. The goal of screening for prostate cancer is to catch the disease in its early stages, when it is more easily treated and before it has spread. The most common screening tests for prostate cancer are the prostate specific antigen (PSA) test and the digital rectal exam (DRE). Transrectal ultrasound (TRUS) may also be used, although its usefulness as a screening test is limited.
If a man has any symptoms or indications of prostate cancer, then he should be tested for the disease and receive follow-up care.
To Screen, or Not to Screen
Prostate cancer screening using PSA testing is almost routine in the US, with almost 60% of men aged over 50 having the test every year. But the issue of prostate cancer screening is a controversial one, and there are arguments to be made both for and against this practice.
Experts who support prostate screening note that there is now evidence from a randomized, controlled trial that shows a decrease in mortality associated with PSA screening. They also note that deaths from prostate cancer have fallen four times more quickly in the US than in Britain since PSA screening was widely introduced in the US. Fewer than 10% of men over 50 are tested annually in the UK.
Those who question the usefulness of PSA screening, on the other hand, note that PSA testing is an inexact test for cancer. For instance, it may indicate the presence of cancer when there is none, or underestimate the aggressiveness of cancer when it is present (see PSA Test below). They say that the lower mortality due to prostate cancer in the US may be due to other factors, such as different treatment practices in the two countries, including the greater use of hormone therapy in older men, as well as the more aggressive treatment of men with locally advanced cancer, in the US.
The most compelling argument against PSA screening is that it may lead to aggressive treatment for prostate cancers that are slow growing and essentially harmless. Aggressive curative treatments for prostate cancer, including surgery, radiation therapy, and cryotherapy, are risky and may have debilitating side effects that can leave a man permanently incontinent and/or impotent.
These are serious considerations. If you are thinking about being screened for prostate cancer, you should consult with your general practitioner or urologist and obtain information on the benefits and shortcomings of PSA screening. After weighing the pros and cons, you can decide whether or not to have it. Men of African descent, and men who have a close relative who was diagnosed with prostate cancer at an early age, should talk with their doctor about being screened starting at age 45. If you do decide to be screened and the results show it is likely you have prostate cancer, bear in mind that most prostate cancers are slow growing. Before undertaking aggressive, invasive treatment, discuss with your doctor the option of active surveillance (see Active Surveillance and Watchful Waiting on the Treatment page). By monitoring the progress of the cancer, you may be able to postpone radical treatment or avoid it altogether.
In the PSA test, a blood sample is analyzed for PSA, a substance normally produced by the prostate that helps to liquify semen. High levels of PSA may indicate the presence of cancer.
But the PSA test is an unreliable indicator. It is possible to have a PSA level under the normal level and still have prostate cancer. What's more, a higher-than-normal level can indicate the presence of prostate cancer, but it can also be a sign of a prostate infection or inflammation, of nonmalignant enlargement of the prostate (BPH), or even of increasing age (PSA levels normally increase with age). PSA levels also rise for a short period of time after ejaculation.
It's also important to remember that PSA levels are relative. For instance, a number that would be abnormally high for a young man might be perfectly normal for an older man, because PSA levels rise with age. African-American men also normally have somewhat higher levels of PSA than do men of other races.
A high level of PSA isn't predictive of whether someone with prostate cancer will have symptoms or not, or how long he will survive. A man can have a high number and be asymptomatic. Conversely, a man can have a low PSA level and still have symptoms of prostate cancer.
There are different systems of measurement, or assays, for PSA. These different assays use different ranges of numbers to show what is normal and abnormal. For instance, Hybritech, the most commonly used assay, has a normal range of 1-4, while the Yang normal range is 0-2.5.
More than 75% of patients with prostate cancer have PSA levels over the normal range. Increasing levels of PSA mean an increasing probability of having cancer. A PSA level of above 10 (Hybritech assay) indicates a greater than 50% chance of having prostate cancer. Very high levels may indicate the cancer has metastasized outside of the gland.
Uses of PSA Tests
In addition to screening, other uses of the PSA test include:
- After diagnosis, the PSA test can be used in conjunction with other tests to help decide on course of treatment.
- During treatment, the PSA test can be used to help show if and how well treatment is working.
- After treatment, the test may show whether the cancer has recurred (come back). In this case, the actual PSA number may be less important than whether it has changed.
- If an active surveillance approach has been chosen, PSA levels can help indicate whether the cancer is growing.
Digital Rectal Exam (DRE)
In a digital rectal exam, the doctor inserts a lubricated finger into the rectum and palpates (feels) it to see if there are any bumps or hard places on the prostate. This can be done because the prostate sits directly in front of the rectum and is separated from it only by the thin rectal wall. It should not be painful. If it is, this could indicate a problem.
A DRE can sometimes find cancers in men with normal PSA levels. For this reason, the American Cancer Society recommends that both the DRE and the PSA test be used in cancer screening.
Other uses of the DRE include:
- After diagnosis, the DRE can help show whether the cancer has metastasized beyond the prostate gland.
- After treatment, the DRE may show whether the cancer has recurred.
Transrectal Ultrasound (TRUS) Exam
Transrectal ultrasound, which utilizes a small probe about the size and shape of a cigar, may be used to obtain a picture of the prostate gland. The image is displayed on a monitor. As a screening tool, TRUS is limited by low sensitivity: it misses 24-30% of cancers that have the same density as the surrounding prostate tissue. However, it is useful in other ways:
- In someone with an elevated PSA level or an abnormal DRE, TRUS can be used to pinpoint the tumor's exact location and assess its size and character.
- TRUS can be used to guide the biopsy needle in order to systematically sample the prostate.
To Test or Not to Test
Screening for prostate cancer is a controversial subject. In general, when a cancer is found early in its course, it is easier to treat. But the PSA test can't determine how aggressive a prostate cancer is. Screening for prostate can lead to the discovery, and treatment, of slow-growing cancers that never would have caused any trouble if they hadn't been found. Surgery and radiation for prostate cancer can have long-lasting, debilitating effects, including impotence and incontinence, which are potentially worse than the long-term effects of the cancer being treated.
Who Should Be Tested?
The American Cancer Society doesn't recommend routine screening for prostate cancer for men at average risk. It does recommend that these men discuss with their doctors the pros and cons of screening, starting at age 50. Men of African descent and men with a first-degree relative diagnosed with cancer at a young age should begin testing at age 45. Men at very high risk (those with several close relatives who developed prostate cancer at an early age) may want to begin screening at age 40, and should discuss this with their doctors.
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