Digital Rectal Exam
Although DRE has been used for many years, careful evaluation of this modality has yet to take place. Several observational studies have examined process measures such as sensitivity and case-survival data, but without appropriate controls and with no adjustment for lead-time and length biases.[7,8]
In 1984, one study reported on 811 unselected patients aged 50 to 80 years who underwent rectal examination and follow-up. Thirty-eight of 43 patients with a palpable abnormality in the prostate agreed to undergo biopsy. The positive predictive value (PPV) of a palpable nodule, i.e., prostate cancer on biopsy, was 29% (11 of 38). Further evaluation revealed that 45% of the cases were stage B, 36% were stage C, and 18% were stage D. More results from the same investigators revealed a 25% positive predictive value, with 68% of the detected tumors clinically localized but only approximately 30% pathologically localized after radical prostatectomy. Some investigators reported a high proportion of clinically localized disease when prostate cancer is detected by routine rectal examination, while others reported that even with annual rectal examination, only 20% of cases are localized at diagnosis. It has been reported that 25% of men presenting with metastatic disease had a normal prostate examination. Another case-control study examining screening with both DRE and PSA found a reduction in prostate cancer mortality that was not statistically significant (OR, 0.7; 95% CI, 0.46–1.1). Most men in this study were screened with DRE rather than PSA. All four of these case-control studies are consistent with a reduction of 20% to 30% in prostate cancer mortality. Potential biases inherent in this study design, however, limit the ability to draw conclusions on the basis of this evidence alone.
Since PSA assays became widely available in the late 1980s, DRE alone is rarely discussed as a screening modality. A number of studies have found that DRE has a poor predictive value for prostate cancer if PSA is at very low levels. In the European Study on Screening for Prostate Cancer, it was found that if DRE is used only for a PSA higher than 1.5 ng/mL (thus, no DRE is performed with PSA < 1.5 ng/mL), 29% of all biopsies would be eliminated while maintaining a 95% prostate cancer detection sensitivity. By applying DRE only for patients with a PSA higher than 2.0 ng/mL, the biopsy rate would decrease by 36% while sensitivity would drop to only 92%. A previous report from this same institution found DRE to have poor performance characteristics. Among 10,523 men randomly assigned to screening, it was reported that the overall prostate cancer detection rate using PSA, DRE, and TRUS was 4.5% compared with only 2.5% if DRE alone had been used. Among men with a PSA lower than 3.0 ng/mL, the PPV of DRE was only 4% to 11%. Despite the poor performance of DRE, a retrospective case-control study of men in Olmsted County, Minnesota, who died of prostate cancer found that case patients were less likely to have undergone DRE during the 10 years before diagnosis of prostate cancer (OR, 0.51; 95% CI, 0.31–0.84). These data suggested that screening DREs may prevent 50% to 70% of deaths from prostate cancer. Contrary to these findings, results from a case-control study of 150 men who ultimately died of prostate cancer were compared with 299 controls without disease. In this different population, a similar number of cases and controls had undergone DRE during the 10-year interval before prostate cancer diagnosis. One case-control study reported no statistically significant association between routine screening with DRE and occurrence of metastatic prostate cancer. The Prostate Cancer Prevention Trial (PCPT) requested all men undergo prostate biopsy at study end to address ascertainment bias; the sensitivity of DRE for prostate cancer was 16.7%. The sensitivity increased to 21.3% in men receiving finasteride.