Don’t Skip Your Digital Rectal Exam
When men discuss screening for prostate cancer with their physicians, some ask: Do I really need the digital rectal exam (DRE)? This physical evaluation allows doctors to check for growths and other abnormalities on the prostate that could signal the presence of cancer, but it also causes anxiety in many men. What’s more, some studies have questioned whether the DRE offers valuable diagnostic information beyond that provided by the prostate-specific antigen (PSA) blood test. Yet other research and the clinical experience of many physicians suggest that pairing these two tests remains the most effective way to screen asymptomatic men for prostate cancer. Here’s a look at both sides of the debate.
A powerful combination
To perform the DRE, a doctor puts on an exam glove and applies lubricant to his or her index finger. Inserting the finger into the rectum, the doctor examines the prostate, feeling for signs of abnormal cell growth, such as nodules (small lumps) or hardened tissue. The exam is brief and painless, though some men find the test uncomfortable and embarrassing.
For many years, the DRE was the primary tool doctors had for detecting signs of prostate cancer. But in 1986, the U.S. Food and Drug Administration (FDA) approved the PSA test, which measures blood levels of an enzyme that rises in men who have prostate cancer, to monitor disease recurrence in patients who had undergone radical prostatectomy.
Research also showed that this simple blood test could more accurately detect prostate cancer at an earlier stage than the DRE-a finding that suggested it might make an effective screening tool. This idea was investigated in a landmark 1994 study published in The Journal of Urology. For the study, 6,630 men aged 50 or older had both a DRE and a PSA test. Men who had suspicious findings on either test had biopsies, which detected prostate cancer in 264 of the men. The PSA tests correctly identified 82 percent of the malignancies, while the DRE detected 55 percent of them. However, the greatest number of tumors could be detected by combining both tests. That same year, the FDA approved the PSA test to screen for prostate cancer in men over age 50 when used along with the DRE.
Soon, pairing the PSA test and DRE as part of a routine physical exam became an accepted strategy for early detection of prostate cancer. In 2012, however, the United States Preventive Services Task Force (USPSTF)-an independent advisory panel of experts in prevention and evidence-based medicine-discouraged routine use of the PSA test for screening. The recommendation was based on concerns that the risk associated with the PSA test outweighed its benefits. Rates of PSA testing fell soon after, and while the USPSTF made no formal recommendation about DREs, rates of that test declined in the United States, too-by 64 percent, according to a 2016 study in The Journal of Urology. In fact, the study found that doctors performed the DRE at less than 6 percent of office visits for preventive care for men 40 and older.
The USPSTF changed its position in 2017 and now advises men 55 to 69 to discuss screening with their physicians, but it’s too early to say whether the new recommendation has had any impact on use of the DRE.
Questions about the DRE
Over the years, some doctors have questioned the DRE’s value as a screening tool for prostate cancer. The test can miss malignant growths that arise on the front or top of the prostate, which are beyond the physician’s reach. What’s more, the DRE is an inherently subjective medical test, since it relies on a doctor’s sense of touch and his or her interpretation of what feels abnormal, which studies suggest canvary widely from one physician to another.
In a 2008 study published in The Prostate, Dutch researchers analyzed data from a large trial that evaluated the benefits of prostate cancer screening. They focused on a half dozen physicians participating in the trial and found that some identified suspicious bumps or spots in relatively few prostates when they performed the DRE, while others found reason for concern in more than a quarter of the men they examined. That suggests a lack of agreement among doctors regarding what constitutes a suspicious DRE finding. Yet this study confirmed the DRE’s value in an important way: All suspicious findings in this study, regardless of which clinician reported them, had a similar likelihood of being identified as cancer by biopsies.
Another large study that examined early detection of prostate cancer, the Prostate, Lung, Colorectal, and Ovarian (PLCO) Screening Trial, also afforded researchers an opportunity to evaluate the DRE. The PLCO included 38,340 men who had annual PSA and DRE exams. Men who had suspicious results on either test were referred for prostate biopsies. Researchers wanted to know how accurately a positive DRE identified men with clinically significant prostate cancer (CSPC), meaning a tumor that posed an intermediate or high risk. They found that 5,064 of the men had abnormal DREs, but normal PSA tests. Of these men, 99 were found to have CSPC. This means that performing the DRE on a man who has a normal PSA test result will only identify an additional 2 percent of serious prostate tumors. Stated another way, the PLCO trial found that a doctor would need to perform the DRE on 1,372 men as part of routine screening to detect one intermediate or high-risk prostate cancer that PSA testing would have missed. The authors concluded that the DRE wasn’t worth performing in men undergoing PSA testing, and the study’s results were widely reported as evidence that men should skip the test.
Catching cancers PSA misses
It’s worth noting that the results of the PLCO trial should be viewed with caution, since it has been criticized for various shortcomings, including the fact that many men who had positive test results never got biopsies and that it included relatively few African-Americans-a group that presumably would benefit from a DRE at screening because they are at increased risk for prostate cancer and tend to have a more aggressive form.
Meanwhile, a 2012 study published in the Canadian Journal of Urology suggests that the DRE sometimes identifies cancers that the PSA test may miss. Researchers analyzed the medical charts of 806 men who were referred for needle biopsies due to an abnormal DRE, elevated PSA results (according to age-specific criteria, which use higher values for older men) or both. Biopsies detected prostate cancer in 306 of the men; 136 had abnormal DREs, but 43 had normal PSA tests. This means that using age-specific PSA values missed 31 percent of prostate cancers in men with suspicious DREs.
DRE still has a role
Because the DRE can find some cancers missed by PSA testing, the American Cancer Society says the test may be included in prostate cancer screening. But other experts, including the author of the UC Berkeley Prostate Disorders White Paper and the UC Berkeley Editorial Board, say the DRE should always be conducted with a PSA test. While a man who has a very low PSA level is unlikely to have prostate cancer, a suspiciousDRE may, nonetheless, indicate the presence of a tumor. Thus, the DRE results provide additional information that is important to consider when discussing whether a man should have a biopsy.
Another benefit: The DRE can also detect rectal cancer (though it’s not a replacement for standard screening for colorectal cancer).