Dutasteride Therapy Does Not Interfere With Clinical Usefulness Of Serum PSA For Detection Of Prostate Cancer

UroToday.com - Dutasteride is a dual 5a-reductase inhibitor (5ARI) used in the treatment of BPH. Both dutasteride and a related drug, finasteride inhibit the transcription of PSA by decreasing the conversion of testosterone to dihydrotestosterone. It is known that doubling the serum PSA in patients taking finasteride provides an accurate determination of their PSA level. Dr. Andriole and colleagues report a similar finding for dutasteride in the May 2006 issue of the Journal of Urology.

A total of 2,802 men with BPH, no evidence of prostate cancer (CaP), a serum PSA level of 1.5-10ng/ml, a prostate volume >30cc, an AUA symptom score >12, and peak urinary flow rate <15cc/second were randomized to 0.5mg dutasteride or placebo daily for 2 years. PSA levels were monitored at baseline and the maximum increase from the lowest (nadir) level achieved to month 24. This was compared with the placebo group and correlated with CaP detection status. Patients had a prostate biopsy for a PSA level of >4ng/ml after doubling the measured PSA level to account for the effect of dutasteride.

Men taking placebo had an expected increase in PSA, reported as an 8.3% increase at the 24 month mark. The dutasteride treated men had a 60% reduction in their PSA, after doubling to correct for treatment.

The incidence of CaP was 3.3% and 1.4% in the placebo and dutasteride groups, respectively, which was not significantly different until after month 15 when the rate increased in the placebo group and remained stable in the dutasteride group. In men diagnosed with CaP, the PSA changes over the 24-month period were 24% for placebo and 37% for dutasteride treated patients. Application of a PSA cutoff of 4ng/ml for performing a prostate biopsy resulted in a sensitivity of 0.804 vs. 0.737 for the placebo vs. dutasteride men, respectively. The corresponding specificities were 0.578 vs. 0.671 for the placebo vs. dutasteride men, respectively.

Analysis of the increase from the nadir PSA level of 0.8ng/ml yielded a sensitivity of dutasteride of 0.548 and a specificity of 0.795. Greater increases in PSA had greater specificity, but lower sensitivity for a CaP diagnosis compared with smaller increases.

These data support doubling the serum PSA level to maintain clinical usefulness for proceeding with a workup for CaP in men on dutasteride.

By Christopher P. Evans, M.D.

Reference:
J. Urol 2006;175:1657-62.
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