miércoles, 30 de mayo de 2012

U.S. Preventive Services Task Force Advises against PSA Screening ▲ NCI Cancer Bulletin for May 29, 2012 - National Cancer Institute

NCI Cancer Bulletin for May 29, 2012 - National Cancer Institute

U.S. Preventive Services Task Force Advises against PSA Screening

Vials of blood The debate about the value and appropriate use of the PSA blood test to screen for prostate cancer is likely to continue for some time.

A long-awaited update from the U.S. Preventive Services Task Force (USPSTF) recommends against
screening men for prostate cancer with the prostate-specific antigen (PSA) test. The task force's 2008 recommendation advised only against screening men aged 75 and older; the update has extended that guidance to include all men.

The recommendation—published May 21 in the Annals of Internal Medicine and on the USPSTF website Exit Disclaimer—does not apply to PSA testing to monitor prostate cancer progression after diagnosis or treatment.

"All men deserve to know what the science tells us about PSA screening: There is a very small potential benefit and significant potential harms," the task force's co-chair, Dr. Michael LeFevre, explained in a statement on the new recommendation.

Based on some of the responses to the recommendation, however, the debate about the value and appropriate use of PSA screening is likely to continue for some time.

Dr. Sushil Lacy, the current president of the American Urological Association, said the organization was unhappy that the task force had failed to revise its recommendation to "more adequately [reflect] the benefits of the PSA test in the diagnosis of prostate cancer."

And in an accompanying editorial Exit Disclaimer in Annals, Dr. William Catalona, director of the Clinical Prostate Cancer Program at the Robert H. Lurie Comprehensive Cancer Center in Chicago, and his colleagues from several other institutions argued that the task force had "underestimated the benefits and overestimated the harms of prostate cancer screening."

Although task force Chair Dr. Virginia Moyer of the Baylor College of Medicine said that the USPSTF recommendation essentially advises physicians not to suggest PSA screening for their patients, she added that there is no disagreement about the need for shared decision-making among patients and physicians.

"We're not saying, 'Don't respond to your patients who ask about screening,'" she said. "Physicians need to have the right information available, so when patients do ask they can give them accurate information and help them make the best decision."

A Tale of Two Trials

The task force relied heavily on findings from two randomized clinical trials of PSA screening: the NCI-funded Prostate, Lung, Colorectal and Ovarian (PLCO) Cancer Screening Trial and the European Randomized Study of Screening for Prostate Cancer (ERSPC).

In January, the most recent update from the PLCO trial, based on 13 years of follow-up in nearly 60 percent of the trial participants, showed that regular PSA screening did not lead to fewer prostate cancer deaths. On the other hand, in the ERSPC trial, men who were screened had an approximately 20 percent lower risk of dying of prostate cancer after 9 years of follow-up.

All men deserve to know what the science tells us about PSA screening: There is a very small potential benefit and significant potential harms.
—Dr. Michael LeFevre
The PLCO and ERSPC trials differed in design, however, and both had shortcomings that may have influenced the findings, the task force acknowledged.

The PLCO trial, for example, had a substantial amount of "contamination." That is, about half of the men assigned to usual care (the control arm) had at least one PSA test during the trial.

Although there was a lower contamination rate in the ERSPC trial, the reduced mortality risk in the screening arm was driven almost entirely by participants from just two of the seven countries involved in the trial: Sweden and the Netherlands. And, Dr. Moyer noted, the vast majority of patients in the screening arms were treated at academic medical centers, while nearly all of those in the control arm were treated in community health facilities. This could have biased the results in favor of the screening arm of the study.

Based on an analysis of these and other studies, the USPSTF concluded that no more than 1 death would be avoided for every 1,000 men aged 55 to 69 years screened every 1 to 4 years for a decade.
The task force also pointed to the potential harms that can occur as a result of screening, such as overdiagnosis, psychological harms of false-positive results, and biopsy-related infections. For every 1,000 men treated, Dr. Moyer noted, 200 to 300 will have long-term problems with incontinence, erectile dysfunction, or both.

Recommendations Criticized

In addition to what they called the "methodological flaws" of the two large screening trials, Dr. Catalona and his colleagues argued that it is still too soon to draw firm conclusions on mortality reduction from either trial because the benefits of screening for a slow-growing disease like prostate cancer may take years to become evident.

And the task force "gave little weight," wrote the editorialists, to a PSA screening trial conducted in Göteborg, Sweden, which had longer follow-up than the PLCO and ERSPC trials, but far fewer participants. That trial—which was part of the larger ERSPC trial—showed a 40 percent relative reduction in mortality in men aged 50 to 64 who underwent regular PSA screening.

PSA screening likely played a substantial role in the 40 percent reduction in prostate cancer mortality in the United States since the early 1990s, around the time when PSA screening began to proliferate, said Dr. H. Ballantine Carter, who directs the active surveillance program for men with prostate cancer at the Johns Hopkins University Brady Urological Institute.

"I don't think you can ignore those benefits," Dr. Carter said.

Dr. Moyer noted, however, that there would have been a substantial lag period, as long as 10 years, before any impact on mortality would have been seen from PSA screening. Nevertheless, a 2008 modeling study funded through NCI's Cancer Surveillance and Intervention Modeling Network, suggested that PSA screening could account for anywhere from 45 to 70 percent of the observed drop in prostate cancer mortality.

Despite the disagreement the recommendations have caused, Dr. Carter believes the end result may be beneficial. "I think this starts a conversation that we needed to have about harms and overtreatment, because for a long time those conversations haven't happened," he said. "I think it will move the field toward more targeted screening."
Carmen Phillips
A Failing Grade The USPSTF makes its recommendations based on a grading system Exit Disclaimer. The task force gave PSA screening for prostate cancer a grade of D, which means the evidence indicates "moderate or high certainty that the service has no net benefit or that the harms outweigh the benefits."
Under the previous recommendation, issued in 2008, PSA screening for men younger than 75 was given an I grade, meaning the task force concluded that the available evidence was insufficient to judge whether screening had a net benefit or harm.
The task force issued a draft of the updated recommendation last fall for public comment, and some who commented suggested that PSA screening be given a C grade, meaning physicians may advise individual patients to have a screening test or treatment because the evidence suggests there may be a small benefit.
But under the task force's rules, "We really didn't have any choice about this recommendation," Dr. Moyer explained. "When we put all of the evidence together, under the most optimistic view, the potential benefit of screening was very small. And the potential harm was substantial. So the net [impact of PSA screening] comes out negative."

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