The debate over whether to treat early stage prostate cancer wages on. New tests may help determine when to treat and when to watch and wait.
Prostate cancer is the most common form of cancer in American men, according to the American Cancer Society, and the prostate-specific antigen, or PSA, blood test has long been the standard for screening men for the disease. In recent months, two major studies—one from Europe and one from the United States—indicated that PSA testing saves few, if any, lives.
In particular, the US study of 77,000 men found there were only slightly more deaths among men who received PSA screening than among those in a control group, who were not screened. According to David Chen, MD, a cancer surgeon at Fox Chase Cancer Center in Cheltenham, Pennsylvania, that does not mean we should stop looking for prostate cancers.
“There’s certainly some categories of men who have very aggressive cancers where finding it early does make a difference, though they’re in the minority,” Chen said. “So, if the bulk of the cancers that are found are going to be less aggressive and somewhat indolent, maybe the focus shouldn’t be on finding every cancer and treating every cancer, as it has historically been, but finding cancers that are more likely to be aggressive and treating those selectively.”
What is becoming increasingly important in prostate cancer research is not just finding the cancer, but being able to determine whether it is benign or aggressive. According to data from a University of Michigan Medical School study, distinguishing between the two might be as simple as testing a patient’s level of sarcosine. Researchers found that levels of sarcosine, a derivative of the amino acid glycine, are considerably higher in patients with aggressive tumors.
“When we start seeing compounds like sarcosine going up, then clearly this tissue is becoming more aggressive. We believe, furthermore, that the sarcosine is actually part of the mechanism for metastases,” said Chris Beecher, PhD, professor at the University of Michigan Medical School. Having this information, said Chen, is extremely important. It means that finding a cancer and choosing to treat it can be two different decisions. Chen said that, fortunately, the adverse effects associated with prostate cancer treatment are, on average, less than they were 10 years ago. “The likelihood of having incontinence or impotence as a side effect of surgery or radiation is much less now,” Chen said. “But, it’s certainly not zero.”
New Screening Options
In December 2008, CombiMatrix Corporation introduced an array-based prostate cancer test. It is based on peer-reviewed studies identifying several genetic tumor markers that enable a more precise stratification of the risk profile of cancer patients. CombiMatrix CEO Amit Kumar, PhD, noted that ongoing studies are discovering specific genetic anomalies in prostate cancer cells. “We know that there are some genes that, if there’s an aberration in that particular gene, then the cancer is aggressive,” Kumar said. “As such, after a doctor has taken a biopsy sample, we can test that sample to look for the specific aberration. If it exists, then the doctor knows the patient has aggressive cancer, and an aggressive approach is needed rather than watchful waiting.”
Aureon Laboratories, Inc. has also introduced a biopsy-based test—Prostate Px—that predicts prostate cancer progression and disease recurrence at the time of diagnosis. According to the company, the test is based on results from a large study that used data and samples from a cohort of 1027 men treated at the Mayo Clinic, Uppsala University, University of Connecticut, and Duke University Medical Center. In validation, the test’s predictive model identified twice as many high-risk events in low- and intermediate-risk patients as the best method available.
Chen said he is familiar with Prostate Px but has had little experience with the test. He does believe, however, that tests of this nature hold the promise of understanding better which men have a more aggressive form of prostate cancer. “It’s a different level of information than what is generally found from existing assessments,” he explained. “It utilizes newer, genetic-based assessments of the cancer tissue as opposed to a blood sample. For most men, that’s not an issue, because they ultimately have a biopsy of the prostate cancer, so the tissue from the biopsy can be used for this type of analysis.”
It is easy to recognize the potential benefits of these new screening tests, said Kumar. “You don’t want to cut someone open and do aggressive chemotherapy that may affect his life and even reduce his life expectancy just because he has prostate cancer. It may turn out that he has the more indolent form.”
The challenge going forward, Kumar added, with regard to this personalized medicine approach, is that physicians have to be taught how to use this new information. “And we have to demonstrate how the information we’re providing is valuable to them.”
Ed Rabinowitz is a veteran healthcare reporter and writer. He welcomes comments at email@example.com.