PSA is impacted by finasteride administration. After 12 mo of treatment with finasteride 5 mg/day, Narayan and colleagues found a mean 43.27% decrease in PSA from baseline values (43). Guess' group in the North American clinical trial found a 50% median decline in PSA values after 12 mo of treatment (44). Moore and associates determined that patients had a 53.76% decline in mean PSA level after 5 yr of finasteride therapy (45).
The decrease in serum PSA levels are generally predictable over the entire range of PSA values, even in those patients with prostate cancer (19). In numerous clinical trials where elevated PSA was closely monitored with serial repeat testing and prostate biopsies, finasteride did not appear to affect the rate of detection of prostate cancer. In fact, in these studies, there was no significant difference in the detection of prostate cancer for patients taking finasteride vs those taking placebo. The PLESS study group, which included 3000 patients, confirmed that in men treated with finasteride for 6 mo or more, PSA results should be doubled for comparison with ranges from untreated men (29).
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