When a prostate-specific antigen (PSA) blood test produces an abnormal result, the following step is normally a prostate biopsy. A biopsy can confirm or rule out a cancer diagnosis, nevertheless it also has some pitfalls. Prostate biopsies are invasive procedures with potential unwanted effects, and so they often detect low-grade, slow-growing tumors that will not require immediate treatment—or any treatment in any respect.
Researchers are exploring different strategies to avoid unnecessary biopsies. Special magnetic resonance imaging (MRI) scans, for instance, will be useful for predicting whether a person's tumor is more likely to spread. A blood test called the Prostate Health Index (PHI) measures different levels of PSA, and can assist doctors determine if a biopsy is required.
In April, researchers from the University of Michigan published Results With a test that screens for prostate cancer in urine samples. Called the MyProstateRating 2.0 (MPS2) test, it looks for 18 different genes related to high-grade tumors. “If you're negative on this test, it's almost certain that you don't have aggressive prostate cancer,” said Dr. Arul Chennaiyin, professor of pathology and urology on the university, in a press release.
Data collection and further testing
To create the test, Dr. Chanayan and his colleagues first turned to a publicly available database of greater than 58,000 genes related to prostate cancer. From this initial pool, they narrowed all the way down to 54 genes which can be uniquely overexpressed in cancers classified as grade group 2 (GG2) or higher. The grade group system ranks prostate cancer from GG1 (least dangerous) to GG5 (most dangerous).
The team tested these 54 genes against stored urine samples with PSA from 761 men scheduled for biopsy. This effort yielded 18 genes that were consistently related to advanced cancer in biopsy samples. These genes now make MPS2.
The team then validated the test by performing MPS2 testing on greater than 800 archived urine samples collected by the National Prostate Cancer Research Consortium. Other researchers affiliated with the consortium reviewed the brand new urine test results against patient records.
Interpretation of results
The results of the study showed that MPS2 appropriately identified 95% of GG2 prostate cancers and 99% of GG3 or higher cancers. The test's accuracy was further improved by including an estimate of prostate size (or volume, because it's also called).
According to the team's calculations, using MPS2 would have reduced unnecessary biopsies by 37 percent. If volume had been included within the measurement, 41% of biopsies would have been avoided. In comparison, only 26% of biopsies with PHI would have been avoided.
Dr. Chanayan and his co-authors emphasize that ruling out advanced cancer with a urine test offers some benefits over MRI. For example, specialized multiparametric MRI scans needed to evaluate advanced cancer in men with elevated PSA are usually not all the time available in community settings. Furthermore, the interpretation of mpMRI results may vary from one radiologist to a different. Importantly, MPS2 will be updated over time as latest prostate cancer genes are identified.
Tafsir
But Dr. Gershman adds that it could be essential to think about how such a test would fit into the present two-step approach to PSA screening, which incorporates a prostate MRI if the PSA is abnormal. Where MRI provides a yes/no result (ie, lesions that look suspicious for cancer are either present or not), MPS2 provides a numerical estimate of risk between 0% and 100%. “The challenge with clinical implementation of consistent risk scores is where to draw the line for biopsy,” says Dr. Gershman.