Historically, the DRE was considered the first-line approach to screening for carcinoma of the prostate. Digital rectal examination has long been a component of routine health screening examinations for middle-aged and older men and is not associated with any additional risks or extra financial cost.11 Abnormalities on DRE associated with cancer and thereby indicating the need for prostate biopsy include induration, asymmetry, or nodules.14,15
While the true sensitivity and specificity of DRE remain undetermined, the positive predictive value of DRE for detecting prostate cancer has been estimated by various studies to be between 15 and 30%.11 Using the presence of nodules as criteria for biopsy, Thompson et al.16 reported a positive predictive value (PPV) of 26% while Chodak and associates detected 36 malignancies in 144 biopsies (PPV of 25%) that were performed based on detection of induration, asymmetry, or nodules on exam-ination.14 In addition, DRE appears to have a low negative predictive value in that the absence of abnormalities on DRE does not appear to considerably reduce the patient's odds of having a clinically significant cancer. Coley et al. suggest that this low negative predictive value is likely due to the low sensitivity of DRE for the detection of prostate cancer.11 Another confounding factor limiting widespread use of DRE alone as a screening tool is limited interexaminer reliability, even among urologists. This is demonstrated by a study by Smith and Catalona showing that DRE findings were disconcordant among examiners for half of cancers.17
Digital rectal examination by itself is a poor screening modality since cancers detected by DRE tend to be advanced and incurable.6 In a study by Thompson et al., 15 of 17 cancers detected by DRE revealed no evidence of metastases based on clinical staging; subsequent pathologic examination, however, resulted in upstaging to advanced, noncurable disease in 66% of cases.16 In addition, Chodak and associates reported that 50% of patients diagnosed with clinical stage B disease based on DRE findings were upgraded to stage C or D1 following pathologic examination of surgical specimens.14
There is a also a lack of data from controlled studies to indicate that screening with DRE alone alters survival from carcinoma of the prostate. In fact, when Gerber and associates examined prostate cancer mortality in men undergoing routine screening with DRE, they found that disease-specific survival was lower for men whose cancer was detected on a subsequent screening DRE than for men whose disease was diagnosed on the initial examination.18 Despite its ease of performance and low cost, therefore, DRE alone has limited, if any, utility in screening for prostate cancer.
Recent data indicate that DRE may be complementary to PSA testing,3 however. When used together this combination represents the most effective screening tool for detecting prostate cancer in its earliest stages.15,19 In a community screening study, Bretton reported that 50% of men with both an abnormal DRE and PSA were found to have cancer at the time of biopsy. This represented a higher positive predictive value than for abnormalities in DRE or PSA alone.19 Similarly, Catalona et al. showed in a study of over 6000 men that the combination of PSA and DRE resulted in a greater than 80% improvement in cancer detection rates over DRE alone.15 More specifically, for patients with a PSA between 4.1 and 9.9 ng per mL, the presence of an abnormality on DRE increased the PPV of the PSA elevation to 49% from 24% with a normal DRE. Moreover, among patients with a total PSA higher than 10.0 ng per mL, the presence of a positive DRE resulted in a 69% PPV versus the 42% PPV seen in patients with a similar degree of PSA elevation but with normal physical exams.15 Similar findings were reported by Brawer and associates.20 In addition, a study by Babaian et al. reported a PPV of 75% for DRE and PSA in combination, compared to 59% and 51%, respectively, for PSA and DRE alone.21 These findings indicate that screening by digital rectal examinations enhances detection of early prostate cancer when performed in conjunction with PSA measurements.
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