How Valuable Is Genetic Testing for Prostate Cancer?
In many ways, cancer is one of the biggest mysteries in medicine. It can lurk in our cells undetected for years. It can strike at any time. And it has no discrimination.
Unlocking the unknowns of cancer is a top priority for many researchers, and one clue to better understanding the disease is genetic testing. In a broad sense, genetic testing represents a method of looking at mutations in your cells to predict your or your family's risk of cancer or guide treatment options with a diagnosis.
For prostate cancer, genetic testing isn't mainstream, but some doctors see value in using it as a tool for treatment now—and in the future.
Two types of genetic testing
Genetic testing for cancer, including prostate cancer, is done through either somatic or germline testing, according to Abhinav Sidana, M.D., MPH, assistant professor of surgery and director of urologic oncology at the University of Cincinnati College of Medicine.
These two types of genetic testing work very differently and have different purposes.
Germline genetic testing
Germline testing looks for mutations in the genes with which you were born, Sidana explained. These are genes you can pass on to your children or might share with your siblings. This testing will check for specific gene mutations, which can determine the type of prostate cancer you have and how aggressive it is, similar to breast cancer genetic testing. Germline testing is done through a blood or saliva test.
Somatic genetic testing
Somatic testing, on the other hand, tests for mutations that have occurred in your genes over time and have now caused cancer. Such mutations could be the result of various factors, including smoking, aging and diet.
"Some men do not have positive germlines but still develop prostate cancer," Sidana said. "Somatic testing will tell us what mutations are in the prostate tissue and can guide treatment options."
Unlike germline testing, somatic testing requires a biopsy from the cancerous area, so with prostate cancer, a biopsy from the prostate would be needed.
The reason genetic testing is used specifically for prostate cancer is twofold. First, although only 5 percent to 10 percent of cancers are hereditary, prostate cancer is the most likely male-specific cancer to be inherited. Second, prostate cancer survivors typically live for many years—the relative 15-year survival rate is 96 percent—allowing researchers more time to study the specific mutations and markers of the cancer.
Genetic screening is a relatively new tool, and research on how it can be best utilized is still emerging, according to Paul Kozlowski, M.D., a urologist and surgeon at Seattle's Virginia Mason Hospital.
A guide for treatment options
As Sidana pointed out, the primary benefit of genetic testing is that the results can help guide treatment options for anyone who receives a prostate cancer diagnosis. Additionally, germline genetic testing can help determine whether they have certain types of heredity genes that any male children or siblings may also have.
Certain types of mutations are associated with specific types of cancers. For instance, someone who tests positive for Lynch syndrome will have an increased risk of also developing prostate cancer. Once you are diagnosed with prostate cancer, germline genetic testing can be done to determine whether the type of prostate cancer you have is hereditary; if testing reveals it is hereditary, you can then inform any family members so they can decide if testing is right for them.
For treatment, Sidana explained that he finds somatic genetic testing most useful after a first-line treatment option, such as surgery, radiation or high-intensity focused ultrasound (HIFU), fails to eliminate the cancer. Somatic testing can help identify the next choice of treatment based on the mutation causing the cancer.
"There are several treatments that can target genetic mutations," Sidana said, adding that somatic testing won't change the treatment course in most cases but can in some situations.
"The odds of the genetic testing making me change what I would do without it are relatively low, and that's why a lot of urologists don't order it," he said. "But in every 20 to 25 patients, I'll find a mutation that would make me say, 'I'll do something different for him.'"
As an example of how this process works, Sidana said genetic testing can identify a specific type of DNA mutation that can then be treated with a medication prescribed specifically for said mutation. The patient becomes eligible for the medication and gets an extra line of therapy, and two treatments can prolong their survival.
Germline testing may also help identify an aggressive mutation in the early stage of treatment. For instance, Sidana noted if the prostate cancer has an aggressive mutation, the doctor may recommend prostate removal right away instead of a less invasive treatment.
Is genetic testing right for you?
As of now, genetic testing for prostate cancer is not performed routinely and isn't available everywhere. Kozlowski does not usually recommend genetic testing to his patients; instead, he focuses on routine screening and awareness of risk factors, such as family history, being African American or having a female family member with BRCA1 or BRCA2 breast cancer.
The American Urological Association's screening guidelines state genetic testing should be done if the prostate cancer is suspected to be aggressive or the prostate-specific antigen (PSA) test indicates a "suspicious" level. PSA is a protein made by both normal and cancerous cells in the prostate gland. High levels of PSA in the blood often indicate early-stage prostate cancer, though that isn't always the case.
Though Sidana conducts somatic testing only after a first-line treatment fails, he believes genetic testing should be more "mainstream." He orders germline testing for everyone diagnosed with aggressive prostate cancer.
Anyone interested in genetic testing should talk to their urologist about germline testing, but only after they receive a prostate cancer diagnosis, because health insurance might pay for it in that situation so the doctor can determine which types of genetic mutations are present. Family members, including siblings and children, can then be tested, too. For uninsured patients, many genetic testing companies will help subsidize the cost, Sidana said.
If you haven't been diagnosed with prostate cancer but are concerned about your risk, first talk to your doctor about getting a baseline PSA and a digital rectal exam (DRE) beginning at age 55, or earlier if you have a family history of the disease, Kozlowski stressed.
Genetic testing might be the future of cancer diagnosis and treatment, but for now, don't skip your routine screening as a first step.