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.

Roughly 30 percent of men could have avoided biopsy if their PSA test results were adjusted to reflect their genetic tendency.

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.

Researchers at the University of California, San Francisco and Stanford University reviewed the total body genetic profiles of more than 95,000 men who did not have prostate cancer to see if they could identify any genetic factors that affect PSA levels. The result: a new scoring tool that measures your likelihood to have a high PSA whether or not you have prostate cancer.

“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.

While the study was very large, almost 90 percent of the participants were of predominantly European ancestry, a key limitation according to Kachuri, because it doesn’t fully reflect the patient population impacted by prostate cancer. “We hope to be able to share findings soon from our efforts to conduct larger and more diverse studies of PSA genetics,” she added.

The study is published Nature.