Prostate Cancer Screening: What We Know, Don't Know, and Believe FREE

Prostate cancer is a devastating illness. Approximately 28 000 American men will die of it this year (1). A method to prevent these deaths is sorely needed. For more than 20 years, many have believed that screening asymptomatic men of a certain age with serum prostate-specific antigen (PSA) is that method. Yet, every medical intervention has some harms associated with it, and we must weigh those harms against potential benefits. Potential harms of PSA screening are well-documented (2), but questions surround the potential benefits: Does PSA-based screening lead to decreased morbidity and mortality? If beneficial, do the benefits outweigh the harms?

After a review of the evidence about both the benefits and harms of PSA screening and treatment of localized prostate cancer, the U.S. Preventive Services Task Force (USPSTF) gave PSA screening a grade of “D” (3). This is a recommendation against PSA-based screening for men of any age. The Task Force makes D recommendations when there is at least moderate certainty that the harms of an intervention equal or outweigh the benefits. Available scientific data suggesting that screening saves lives were inconsistent. Consequently, the USPSTF determined that, even assuming that available data show that screening saves some lives, the number of lives saved is, “at most, very small” and the proven risk for harm outweighs any potential benefit.

In October 2011, the Task Force's release of a draft recommendation for public comment caused many clinicians and patients to express outrage (4). Undoubtedly, the final recommendation, which is unchanged after consideration of public comment, will upset many in the prostate cancer advocacy community. Lost in the heat of last fall's rhetoric was the fact that the Agency for Healthcare Research and Quality commissioned an independent group of experts in evidence appraisal to systematically review the world's literature on prostate cancer screening and treatment (2,5). The Task Force, a second independent group with expertise in preventive medicine and screening, then considered the systematic review when formulating its clinical recommendation. The USPSTF is ideally suited to provide an objective, unbiased assessment of the state of the science. Unlike many of their critics, the Task Force members have no emotional, ideological, or financial conflicts of interest. And, of note, unlike some of its most vocal critics, the Task Force understands the complicated science of screening.

I believe that much of the shock about this recent recommendation is because Americans have been taught for decades to fear all cancer and that the best way to deal with cancer is to find it early and treat it aggressively. As a result, many have a blind faith in early detection of cancer and subsequent aggressive medical intervention whenever cancer is found. There is little appreciation of the harms that screening and medical interventions can cause.

Overdiagnosis makes screening seem to save lives when it truly does not (6). Cases of overdiagnosed cancer fulfill histologic criteria for cancer but are not destined to progress and kill within the patient's natural lifetime. Yet, when detected through screening, these tumors are commonly treated, exposing patients to the harms of treatment without any true associated benefit. The man with such cancer often believes that screening and treatment saved his life, but he would have been just fine had the cancer never been detected and treated. Overdiagnosis also increases the proportion of patients surviving 5 and 10 years. Lead-time bias increases apparent survival rates. Because screening diagnoses some patients earlier, they live longer after cancer diagnosis, even though they do not live longer than counterparts with similar cases of cancer that were not screen-detected. Overdiagnosis was known to be an issue in prostate cancer well before screening became popular. In the 1980s, the respected prostate cancer expert Dr. Willet Whitmore said that the quandary in prostate cancer is, “If cure is necessary, is it possible, and if cure is possible, is it necessary?” (7).

The screening literature stresses a difference between mass screening, in which large numbers of men are tested at an event, and screening within the physician–patient relationship. Much of my own concern about prostate cancer screening has been with mass screenings that mislead men to believe that screening can only help them. Over the past 20 years, celebrities, athletes, politicians, and prostate cancer survivor groups have endorsed screening. Mass screening is commonly conducted in shopping malls, churches, and community centers; at conventions and state fairs; and even in vans parked in grocery store parking lots. Hospitals, medical practices, fraternities, politicians, radio stations, television channels, and even an adult diaper manufacturer have sponsored mass prostate cancer screenings. Promotions for these events frequently discuss the high proportion of men with screen-detected tumors surviving 5 years and sometimes claim that screening saves lives. They never mention the potential harms of screening. Many well-meaning persons have supported screening activities and chose not to listen or believe those who have urged caution about screening. Mass screening is also a lucrative business. As Upton Sinclair once said, “It is difficult to get a man to understand something, when his salary depends on his not understanding it” (8).

It is my hope that the current USPSTF recommendation ends mass screening. Although recommending against routine screening, the Task Force does leave room for it within the physician–patient relationship. They recognize that there are men who will still want to be screened because of family history, ethnicity associated with prostate cancer risk, or a special concern. They also recognize that physicians will want to provide screening to some patients. However, the Task Force wisely emphasizes that these physicians have a special obligation to ensure that the patient understands the proven risks and the unproven benefits of PSA-based screening.

Many professional organizations have made prostate cancer screening recommendations in the past few years that urge caution and informed or shared decision making. The American Cancer Society did advocate routine annual screening in the early 1990s but backed off and began recommending informed decision making in 1997 (9). Today, the American Cancer Society statement supports informed decision making and acknowledges the potential for harm. Other organizations, such as the European Association of Urology and the National Comprehensive Cancer Network, also recognize the harms of screening and call for men to be informed before making a decision about screening (10 - 11). The American Urological Association has, at times, been very pro-screening, but has stated in its 2009 PSA Best Practice Statement, “Given the uncertainty that PSA testing results in more benefit than harm, a thoughtful and broad approach to PSA is critical. Patients need to be informed of the risks and the benefits of testing before it is undertaken. The risks of over-detection and over-treatment should be included in this discussion” (12). Although the Task Force statement is more pointed than those of other expert organizations, it is not incongruent with those recommendations. Yet, many advocates for prostate cancer screening have ignored the messages of caution of other organizations and continue to encourage screening without caveats. Informed or shared decision making is simply not occurring (13).

We must heed science when making clinical and policy decisions about PSA-based prostate cancer screening. The harms are well-proven, whereas the evidence of benefit is weak. Even if one accepts that true benefits exist, the documented harms are probably greater than those small benefits. Despite this, some will continue to forcefully advocate PSA-based screening because of a blind faith in early detection. We need to practice medicine on the basis of evidence and not on the basis of faith.

This article was published at www.annals.org on 22 May 2012.