Prostate cancer is the second most common cancer in men, topped only by skin cancer. One of every eight men will be diagnosed with it. What’s most concerning is that since 2014, the number of cases has steadily increased by 3 percent each year, probably because of better and more widespread screening, which is good.
Prostate cancer is typically first suspected when a blood test for PSA (prostate screening antigen) shows rising numbers. Though there is no consensus cutoff level, most doctors will start to monitor patients when the PSA goes above 2.5-3.0 ng/mL.
The PSA test results can, however, be influenced by many factors aside from cancer. Older age, an enlarged prostate, taking testosterone, an infection of the prostate (prostatitis), ejaculation within a few days of the blood test, and even riding a bicycle can sometimes raise the PSA. So, there’s been a long-standing need to improve the accuracy of the test.
Roughly 30 percent of men could have avoided biopsy if their PSA test results were adjusted to reflect their genetic tendency.
“The polygenic score captured each individual’s genetic predisposition to high PSA levels,” said Rebecca Graff, ScD, UCSF assistant professor in the Department of Epidemiology & Biostatistics and one of the senior authors of the study.
The researchers then tested their new scoring system on a group of Kaiser Permanente members, adjusting each participant’s PSA values based on his unique genetic profile. “PSA values personalized in this way are more likely to reveal changes in PSA due to prostate cancer because they are corrected for the influence of inherited genetics,” Kachuri explained.
Personalized PSA values improved the accuracy of prostate biopsy referral decisions. Roughly 30 percent of men could have avoided biopsy if their PSA test results were adjusted to reflect their genetic tendency. One caveat: these adjusted PSA levels would have missed approximately 9 percent of positive, usually low-grade, prostate cancer.
“We showed that genetic correction of PSA levels has the potential to both reduce unnecessary biopsies and improve our ability to detect tumors with a more aggressive profile,” commented Kachuri. The team hopes their findings are a step toward reducing a diagnostic gray area in PSA screening.
The study is published Nature.