Urine test for prostate cancer: Study

By Dr. Ananya Mandal, MDAug 4 2011

According to researchers, a new urine test might help doctors detect prostate cancer and better evaluate a patient's treatment options.

Lead researcher Dr. Scott Tomlins, a pathology resident at the University of Michigan Health System said, “This is a tool that men and their physician can use to help them decide whether it's appropriate to get a biopsy now or delay that decision.” He explained that the test looks for two genetic markers associated with prostate cancer. The first, called TMPRSS2:ERG, is caused by two genes changing places and fusing together; it is thought to cause prostate cancer. Since the gene fusion is only seen in about half of cancer patients, the test also looks for another marker, called PCA3. Tomlins said, “We are exploiting some new bio-markers to try to refine the PSA [prostate-specific antigen] test.”

The PSA test can indicate prostate cancer, but it is unreliable, often producing false positives and false negatives, Tomlins said. “You can have low PSA and have cancer, or high PSA and not have cancer,” he explained. “The two genetic markers may be more reliable indicators of prostate cancer, he said. One of them, TMPRSS2:ERG, is only seen in cancer,” he added.

He added that the two markers together can be used “to stratify men into saying, ‘You have a high chance of having cancer, and you should get a biopsy now, or if you are in a lower risk group you have a much lower risk of cancer and perhaps you could delay the biopsy,’” He warned that the test is not perfect. “It's hard to recommend that someone not get a biopsy, because there is always a chance you are going to miss a cancer that doesn't have either of these two markers,” he said.

For the study, published in the Aug. 3 issue of Science Translational Medicine, Tomlins' team studied urine samples from 1,312 men who had high PSA levels and had had a prostate biopsy or surgery to remove the prostate. They looked for the two markers and used them to slot the men into high-, intermediate- or low-risk groups for prostate cancer. They then compared their results with the results from biopsies, which are done with a needle in a physician's office for detection of any cancer cells.

Biopsy results showed that cancer was found in 21 percent of the men in the low-risk group, in 43 percent of the intermediate-risk group and in 69 percent of the high-risk group. The findings of the urine tests also correlated with tumor size and the cancer's aggressiveness. In the low-risk group, only 7 percent had aggressive cancer, compared with 40 percent of the men classified as high-risk, they found.

One limitation of the study is that most patients were Caucasian, so further studies are needed to see whether the findings extend to all men, the researchers noted. Although not yet available to the public, the test soon will be offered at the University of Michigan, Tomlins said. The test is licensed to Gen-Probe, a San Diego maker of genetically based diagnostic tests. Mike Watt, a company spokesman, said the test is still in the early stages of development and has not been submitted to the U.S. Food and Drug Administration for approval. The company has no firm idea of the test's cost should it be approved, Watt added. Study funding was supported in part by Gen Probe, and the University of Michigan and Brigham and Women’s Hospital have obtained a patent on the detection of ETS gene fusion in prostate cancer, in which four co-authors are listed as co-inventors.

According to prostate cancer expert, Dr. Anthony D'Amico, chief of radiation oncology at Brigham and Women's Hospital in Boston the test is “a step forward, but we still have a ways to go.” D'Amico said, “On average the risk is higher in people with both markers and lowest in people who have neither, but that's on average.” If a patient has indications of an aggressive prostate cancer, the test can add more to that diagnosis, D'Amico said. But for men who potentially have cancer, a low-risk determination based on this test shouldn't preclude biopsy, he said. More than 1 million men have their prostates biopsied every year in the U.S.