Prostate Specific Antigen

Prostate-specific antigen is the best single test for early diagnosis of prostate cancer and, along with DRE, has recently received FDA approval as an aid in the detection of prostate cancer in men 50 years of age and older.10 Since its introduction as a clinical marker nearly two decades ago, PSA has had a profoundly favorable impact on diagnosis and treatment of prostate cancer. The PSA produced by prostatic epithelial cells is not only secreted into prostatic fluid but enters the systemic circulation.3 In serum, PSA is primarily bound to the protease inhibitor a 1-antichymotrypsin, and only a small fraction exists in an unbound or free form.22 Currently, the most frequently used assays measure total serum PSA, including both PSA bound to a 1-antichymotrypsin and unbound PSA.

The findings from six PSA-based prostate cancer screening studies15,20,23-26 are shown in Table 9-1. These results indicate that 8 to 15% of men who are older than

50 years of age will have an abnormal total serum PSA (> 4.0 ng per mL) on initial screening and that cancer will be detected in 1.5 to 4.1% of these patients. Based on follow-up biopsy results, the PPV of an elevated total PSA ranges from 11 to 34%. The false-positive elevations in serum PSA may have been due to one of a number of benign pro-static conditions or prostatic manipulations that have been shown or are speculated to produce elevations in total serum PSA to levels exceeding the threshold for suspicion of malignancy.

Benign prostatic hyperplasia (BPH) is a common condition in men over 50 years of age and has been demonstrated in several studies to produce elevations in total serum PSA that overlap with levels associated with malignancy.27,28 In fact, Nadler et al. reported that prostate volume was the most important benign contributor to PSA elevation.28 The authors also reported that both acute and chronic prostatic inflammation accounted for some elevation in total PSA.28 Reports on the effects of ejaculation on PSA levels have been conflicting to date. Herschman et al. reported a statistically significant elevation in total PSA for up to 24 hours following ejaculation and concluded that PSA measurements within this interval may lead to inaccurate interpretation of both total and free PSA levels.29 In contrast, Stenner and associates found an initial postejaculation fall in PSA levels followed by a return to baseline over 12 hours. These authors concluded that ejaculation has no clinically significant impact on PSA levels and that patients need not abstain from sexual activities prior to PSA screening.30

The effect of finasteride on PSA levels is better defined, as several studies have shown that it lowers total serum PSA levels by 50% on average.31 Recently, Andriole et al. reported data demonstrating that doubling the total PSA level for men receiving finasteride preserves the sensitivity and specificity of PSA testing.32

Although false-positive results are possible, the risk of prostate cancer has been clearly and consistently shown to rise with total serum PSA levels, making this an efficacious test for prostate cancer screening.20,33 In a large multicenter trial reported by Catalona et al., the PPV for prostate cancer when the PSA was between 4.1 and 9.9 ng per mL was 26%

TABLE 9-1. Results from Prostate-Specific Antigen-Based Prostate Cancer Screening Trials

Author

Initial PSA Elevation (%)

Cumulative Cancer Detection Rate (%)

Catalona23

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