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New prostate cancer tests may end overtreatment (PDF, 641 KB) »
In recent years, the field of prostate cancer testing has changed rapidly. William J. Catalona, MD, the scientist who helped bring the PSA test to market more than 20 years ago, compares this fast pace to advancements in cellphone technology. Routine PSA screening, a simple blood test that measures the levels of a protein called prostate specific antigen, is still considered beneficial in finding cancers in earlier stages. However, it does not differentiate between lethal and benign tumors. As a result, thousands of men each year undergo unnecessary biopsies, operations and radiation treatments.
Routine PSA screening … does not differentiate between lethal and benign tumors.
In 2011, the U.S. Preventive Services Task Force stirred up a furor when it recommended against PSA screening in average-age men who had no signs of prostate cancer. Just this year, the American Urological Association and the American College of Physicians issued similar guidelines. Meanwhile, there has been a shift toward more targeted screening as well as the development of advanced tests that distinguish dangerous tumors from benign ones.
Serious nature of the disease
Prostate cancer is the most common cancer in men worldwide and the second most common cause of death by cancer in men. The American Cancer Society estimates that 238,590 new cases of prostate cancer will be diagnosed this year, and 29,720 men will die of the disease. Additionally, according to the American Cancer Society:
Several companies have come out with tests that measure multiple genes, or molecular markers, rather than a single protein such as PSA. They aim to identify tumors that may become lethal, helping doctors and patients make more informed decisions.
Among these companies are Genomic Health and Myriad Genetics, both of which have developed similar genetic tests for breast cancer.
“81 percent of prostate cancer patients with lower [Polaris] scores had an excellent five-year survival rate … even if they were not treated.”
A study published last year in the British Journal of Cancer examined the value of Myriad’s Polaris test in needle biopsy material. Researchers looked at 349 prostate cancer patients who had been diagnosed by needle biopsy and managed conservatively. The Polaris test measures molecular markers in the blood to determine which cancers are likely to become aggressive.
Using a scoring system, researchers found that 81 percent of prostate cancer patients with lower scores had an excellent five-year survival rate of 93 percent even if they were not treated. Among those with higher Polaris scores, the five-year survival rate was only 63 percent and the 10-year rate was 44 percent.
The authors of the study concluded that the Polaris test could provide better information than the Gleason score, the main tool now used to assess tumor progression. Gleason grading is based on how prostate glands look and are organized under a microscope.
The downside of these tests is that they are very expensive, costing around $3,400, and insurers may not want to pay for them because some men may choose to undergo treatment even if the test shows their cancers are not likely to progress.
For more information, see:
• Kentucky Lung Cancer Research Program, Markey Cancer Center, UK HealthCare • What is cancer? Cancer overview • What causes cancer? • How is cancer diagnosed? • About clinical trials: information from the National Cancer Institute
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There have been missteps and problems with PSA testing in the past, but PSA testing has changed the face of prostate cancer. Although the projection is for 239,000 new cases in the United States in 2013, there has been a 30 percent drop in the number of deaths.
“You could argue that the reason the death rate has gone down is PSA screening or better treatment. It’s probably a combination of both.”
Before PSA screening came into use, doctors were finding a high percentage of advanced prostate cancers because the only means of detecting the disease was by rectal exam. You could argue that the reason the death rate has gone down is PSA screening or better treatment. It’s probably a combination of both. Because of this test, we’re detecting these cancers at a much earlier stage, but many may not be harmful.
Prostate cancer is very slow growing. In fact, many men with the disease will die of other causes rather than this cancer. So the question often becomes, if a nonlethal cancer is found in a person in his 70s, which is worse – the expense and side effects of treatment or the disease?
We know we have a killer disease, but not all prostate cancers are deadly. The expense of treatment is huge, and current treatments may impact quality of life.
There are a couple of tests that can be used in combination with the PSA: the PCA3, which detects anomalies of this cancer gene; and the RSS2:erg test, which looks for the presence of this gene-fusion anomaly. The RSS:erg gene fusion is found in roughly 50 percent of prostate cancers. These tests can be performed after a PSA test. Doing them independently is not ideal. They are most useful in patients with higher PSA levels. We can also use variations of the PSA test, such as age adjustment.
Two important trials in recent years on the efficacy of PSA testing had different findings: The PLCO (Prostate, Lung, Colorectal and Ovarian) trial in the United States and the ERSPC (European Randomized Study of Screening for Prostate Cancer) trial in Europe.
The PLCO trial determined there was no benefit from the PSA test and it was in fact harmful. According to the ERSPC, the PSA test is beneficial, resulting in a 20 percent death reduction. The European trial (ERSPC) was actually better designed. With periodic updates of the subjects, the researchers found screening became even more beneficial.
PSA screening does make sense. However, some cancers may not need immediate treatment. In those cases, research has found that doctors can take a watchful-waiting approach: We monitor the patient’s PSA levels and repeat biopsies to determine whether they may need treatment.
The Polaris test, developed by Myriad Genetics, looks at housekeeping genes, which control cell function in the prostate. When you see the activity of those genes you can predict the progression risk of the cancer and whether it might become harmful.
The Genomic Health test, Oncotype DX, is similar. Both tests examine the genetic activity of the patient’s tumor, so doctors can sort out by scores the risk of progression of the cancer. These tests are trying to predict the outcome of the tumor, while the PSA test simply indicates that a tumor may be present.
At present, the tests aren’t widely available because most insurance companies have not decided whether to pay for them. I don’t think they are ideal for routine screening. A better role might be using them to determine susceptibility to certain therapies. Similar tests have been used that way for breast cancers.
They are intriguing tests because they may help us sort out and monitor the patients who have low-risk tumors that don’t require immediate treatment. We are overtreating a lot of these patients now, but if we stop screening altogether we’ll go back to the way things were 25 years ago – patients presenting with much more advanced disease.
The goal is to turn prostate cancer into a chronic disease much like diabetes. In recent years, there have been several new medications that have come along. It used to be that treatment was hormone therapy followed by chemotherapy. Now you have new options for treating prostate cancer that has progressed. Several new drugs and a vaccine are available for use before you even get to chemotherapy, which has also improved.
It still makes sense to screen for prostate cancer, but we need to find better treatments. If a patient has a very low-risk prostate cancer, he should have a discussion with his doctor about what options are available. For someone who is 50 and doesn’t want to gamble, there are standard treatments such as radiation. There are also new treatments being investigated that target small cancers rather than treat the entire prostate.
However, in many of these cases, we could just monitor the disease, and the patient would be fine. We really need to find a reliable “crystal ball” type test that will identify patients at risk for death from their disease or find that solid “safety net”; namely an effective cure/control for advanced prostate cancer that would take the risk out of monitoring lower risk disease.
Dr. Strup is a member of the genitourinary and prostate cancer team at the UK Markey Cancer Center. He also serves as chief of urology at the UK College of Medicine.