By Nancy Lapid

Oct 24 (Reuters) - A decline in prostate cancer screening has been linked to subsequent increases in advanced cancers, according to data from the U.S. Department of Veterans Affairs $(VA)$, findings that may spur revisiting current U.S. testing guidelines.

A new study, involving more than 5 million men over age 40 at 128 VA facilities across the country between 2005 and 2019, found that when screening was encouraged, later diagnoses of incurable advanced malignancies were less likely.

"Screening rates were significant predictors of metastatic cancer rates," study leader Dr. Brent Rose of the University of California, San Diego said at a news conference on Monday at the annual meeting of the American Society for Radiation Oncology (ASTRO) in San Antonio, Texas. Metastatic cancers are those that have advanced and spread to other parts of the body.

The benefits of screening for prostate cancer have been controversial. In 2012, the U.S. Preventive Services Task Force (USPSTF) advised against it, maintaining that because the disease usually progresses very slowly, the risks of screening outweigh the potential benefit. There was concern that suspicion of prostate cancer based on a common blood test could lead to painful, potentially risky biopsies that may not have been necessary.

In 2018, based on new evidence, the panel modified its recommendation to limit prostate cancer screening to men ages 55 to 69, and then only if they "express a preference for screening after being informed of and understanding the benefits and risks."

Overall at the VA facilities, rates of screening with blood tests for prostate-specific antigen $(PSA.AU)$ levels dropped from 47.2% in 2005 to 37.0% in 2019, the researchers reported.

During that period, metastatic prostate cancer rates rose from 5.2 per 100,000 men to 7.9 per 100,000, with the rise driven by increases in the 55-69 and over-70 age groups, the researchers said.

At individual facilities, higher rates of screening were linked with lower rates of subsequent diagnoses of advanced cancers. But for every 10% decrease in screening, there was a corresponding 10% increase in metastatic prostate cancer incidence five years later, the researchers said.

Observational studies like this one cannot prove cause and effect, and earlier randomized trials comparing screening to no screening have yielded conflicting results, further complicating the issue. A large European trial found a significant benefit, but a North American trial did not.

In the North American trial, however, many of the men assigned to the no-screening group "surreptitiously" were screened privately by their personal physicians, which likely biased the outcomes, ASTRO president-elect Dr. Jeff Michalski of Washington University School of Medicine in St. Louis said at the news conference.

Rose noted that while the USPSTF advice to limit prostate cancer screening has resulted in lower rates of prostate cancer diagnoses, rates of metastatic prostate cancer have increased "more dramatically."

"We hope this data will give the USPSTF a chance to re-evaluate their recommendations," Michalski said.

(Reporting by Nancy Lapid; Editing by Michele Gershberg and Bill Berkrot)

((Nancy.Lapid@thomsonreuters.com))