March 20 (Bloomberg) -- It may take a decade to replace the prostate cancer test that doctors say is inadequate and risky, yet is used on 75 percent of American men 50 or older.
The PSA cancer-detection test may only prevent deaths in about 7 in 10,000 males with the disease, according to research reported March 16. The exam often leads men without lethal cancer to undergo unneeded treatment that can result in sexual impotence or incontinence, said Gerald Andriole, chief of urologic surgery at the Washington University School of Medicine in St. Louis.
At least four new tests are being studied in people, said Sudhir Srivastava, chief of the biomarkers research group at the National Cancer Institute in Bethesda, Maryland. The research, aimed at distinguishing slow-growing cancers that rarely cause death from malignancies that can spread and kill, will take “at least 10 years” before they’re in common use, said Christine Berg, also at the NCI. In the meantime, scientists are tweaking the current test to make the results more precise.
“The challenge we have right now is, when we find cancer we don’t know if it is a killer cancer or a toothless lion,” said Andriole, who led one of the two March 16 studies on the test, in a telephone interview.
In the U.S., 28,660 men die from prostate cancer each year, and 186,320 men are diagnosed with it, according to the American Cancer Society.
PSA Increases
The existing test measures prostate specific antigen, or PSA, a blood protein that reflects damage to the prostate. PSA levels rise when prostate cancer develops. They also increase with age and when men develop benign conditions, including enlarged prostate glands or a urinary tract infection.
When men get an elevated PSA result, ruling out cancer requires extracting a piece of the prostate, a gland that weighs less than an ounce and is located below the bladder and in front of the rectum. It secretes fluid that helps semen travel during ejaculation.
The biopsy, a procedure most often done using a needle pushed through the wall of the rectum, costs about $2,400, according to Elizabeth Streich, a spokeswoman for Columbia University Medical Center in New York. In a biopsy, a surgeon removes a tiny piece of prostate tissue so that doctors can examine cells under a microscope for the presence, type and aggressiveness of cancer.
A biopsy’s reliability can also be questionable because it “is prone to being subjective, according to who reads the slide,” Srivastava said.
Genetic Markers
Three of the tests now being studied in humans use genetic markers to differentiate between slow-growing and potentially lethal cancer, the NCI’s Srivastava said. Two would be used to screen urine, another is a blood test, and the fourth would be used in a biopsy to offer a more precise measurement of genetic activity leading to metastasis, the process that spreads cancer throughout the body.
Arul Chinnaiyan, a researcher at the University of Michigan in Ann Arbor, is working with privately held Metabolon Inc., a diagnostic screening company based in Durham, North Carolina, on a test for an amino acid called sarcocine that rises when prostate cancer is active, according to the company.
Metabolon’s test would screen urine to check the severity of a prostate tumor, said John Ryals, Chief Executive Officer of Metabolon, in a telephone interview today.
“One of the problems with PSA is that it doesn’t really tell you much about whether you really have cancer or not and how aggressive a tumor is,” Ryals said. “Sarcosine is involved in the transition of a tumor going from a non-invasive state to a more invasive state.”
Urine, Blood Tests
The National Cancer Institute is working with University of Michigan researcher John Wei on a study analyzing urine samples from patients in Ann Arbor, Boston and Baltimore, seeking a biomarker called PCA3, the NCI’s Srivastava said. PCA3 is a snippet of genetic material that is overproduced in prostate cancer cells.
The blood test being assessed in humans is looking for two genes that fuse together once cancer becomes present. The genes are a marker that the cancer is spreading, according to Srivastava at the NCI, which is collaborating on the research. About 200 volunteers are involved in the research being undertaken at the Veterans Administration Hospital in San Diego, Srivastava said.
A fourth method would examine prostate tissue sample taken during biopsy for a gene called GSTPi1 that can act as a switch, turning on the growth process linked with cancer. Quest Diagnostics Inc., based in Madison, New Jersey, is working with Epigenomics AG in Berlin to develop genetic tests for GSTP1 that would help detect disease activity, the companies said in a statement.
Predicting Behavior
“I am hopeful, although I don’t know when it will come, that if we understand the genetics of cancer we’ll be able to predict its behavior,” said Philip Kantoff, chief clinical research officer and chief of solid tumor oncology at the Dana Farber Cancer Institute in Boston.
While testing on new genetic models continues, researchers are working on ways to make the present PSA test more effective. One way may be to weigh a man’s basic PSA score against how fast the number rises over time, according to the NCI’s Berg.
Combining that information with a patient’s age, the size of his gland, and whether the PSA the protein is floating free in blood or bound to other proteins may improve the accuracy of the test over time, Berg said. Elevated PSA in men in their 40s, before age-related damage is inflicted on the prostate, can also predict cancer rates a quarter century later, Andrew Vickers, a specialist in molecular markers and surgical research results at Memorial Sloan Kettering Cancer Center in New York, said.
Really Tell Risk
“With a single PSA test at an early age,” weighed in relation to other factors, “you can really tell who is at risk for cancer,” Vickers said in a telephone interview.
Beckman Coulter Inc., a Fullerton, California-based diagnostics company, is working with the Cancer Institute and several universities in developing a second blood test to detect another form of PSA, called ProPSA, which reacts differently to the presence of cancer, Srivastava said.
Berg, chief of the National Cancer Institute’s early detection research group, said these adjustments to the standard PSA test could be available in the next few years yet are likely to produce only incremental improvements to accuracy.
“A truly new test will take much longer,” she said.
To contact the reporter on this story: Michelle Fay Cortez in Minneapolis at mcortez@bloomberg.net
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