Exosome-based Urine Test for High-grade Prostate Cancer
Can a home or office urine test replace traditional biopsy?
Lori Malone
For men who have an elevated prostate-specific antigen (PSA) score on initial screening, poor compliance with physician recommended-biopsy is a common issue. Many men simply don't keep their biopsy appointments because of the discomfort and potential complications associated with the procedure, and many prostate biopsies are low-grade or benign and perhaps unnecessary.
To help address these issues, Duke urologists are using the ExoDx Prostate Test (Bio-Techne, Minneapolis, MN), an exosome-based urine test that does not require a digital rectal examination. The test analyzes cancer-specific genomic biomarkers found in the urine to produce a score that helps physicians and patients decide if biopsy is necessary.
Judd W. Moul, MD, a urologic oncologist and internationally recognized prostate cancer expert, says that in general, men are not as compliant with their health care as most women. "Some men avoid going to the doctor because they dread the rectal exam prostate check," he says. "Having a simple urine test as a secondary screen for elevated PSA is very appealing to some men, and anything I can do to improve care is welcome."
Exosomes are released by all living cells into biofluids that contain ribonucleic acid (RNA), deoxyribonucleic acid (DNA), and protein, which are excellent for diagnostic needs, Moul explains. The ExoDx test analyzes a patient's biology in real time through a urine sample, searching for three RNA biomarkers (PCA3, ERG, SPDEF) that are linked to high-grade prostate cancer.
The resulting test score represents a continuum of risk, ranging from 0 to 100. The higher the score, the higher the probability of high-grade prostate cancer. "The score enables a physician-patient shared decision on next steps, removes subjectivity, and improves objectivity. When we have these discussions, we find that patients are less likely to walk away altogether," says Moul.
Moul says the test is well suited for men ages 50 and older with a PSA of 2-10 ng/mL who are being considered for prostate biopsy. It helps avoid biopsy when it's unnecessary and more strongly encourages men to move forward with biopsy when indicated. Other factors Moul considers when deciding on next steps include:
prostate size/existence of benign prostatic hyperplasia
history of prior negative tests and PSA measurements
patient concerns
For men who prefer not to come to the hospital or clinic for the test, urologists can order an at-home ExoDx test, similar to an at-home colon cancer screening test. "This has been especially useful during the COVID-19 pandemic," says Moul. "We can do a telehealth visit with the patient and then order the test kit to be sent to their home if clinically indicated."
Referring to Duke
Because many PCPs no longer perform digital rectal exams due to difficulty in assessing prostate size, and because many PSA scores occur in "gray" zones that aren't well defined, it's not always clear when a PCP should refer a patient to a urologist. Moul says Duke is working to deploy the ExoDx test to Duke Primary Care practices, which will help improve early detection of potential cancers, streamline visits, and help practices utilize resources more effectively.
Moul and his resident colleague, Gabrielle McNary, MD, are currently working to publish data from a Duke study on the effectiveness of the ExoDx test. A large percentage of the study participants have also had a Prostate Health Index (PHI) blood test, so the results will compare the effectiveness of both tests in a highly diverse population.
Urology CMEs
Judd W. Moul, MD
Urologic Oncologist