PURPOSE: To prospectively determine the effect of short-term therapy with dutasteride on the suppression of Doppler ultrasonographic (US) signal in benign prostate tissue and thus on improvement in the depiction of prostate cancer with Doppler US-guided core-needle biopsy. MATERIALS AND METHODS: After institutional review board approval and informed consent were obtained as part of this HIPAA-compliant study, 11 men (age range, 59-77 years) were evaluated with gray-scale, color, and power Doppler US at baseline and weekly for up to 3 weeks while taking 0.5 mg of dutasteride per day. Flow intensity in the periurethral, transition, and peripheral zones was subjectively scored by using a four-point scale. The Wilcoxon matched-pairs signed-ranks test was used to compare pre- and posttherapy scores. After flow was reduced to "diminished" or "none" with at least a 1-score difference on the four-point scale, up to four targeted cores were obtained from areas of persistent flow within the peripheral zone, followed by laterally directed sextant biopsy. RESULTS: Doppler US flow suppression occurred in 11 of 11 patients after 1 week of dutasteride therapy (P < .01). Further suppression was noted after 2 weeks in eight of 10 patients (P = .04) and after 3 weeks in two of two patients. Biopsy was performed after 1 (n = 1), 2 (n = 8), or 3 (n = 2) weeks of therapy. Flow suppression was greatest in the peripheral zones (mean decrease: 0.64 and 0.76 after weeks 1 and 2, respectively) and least in the periurethral zones (mean decrease: 0.30 after 1 week). Cancer was detected in eight (20%) of 40 targeted cores and in five (8%) of 66 sextant cores. Four patients had cancer at targeted biopsy, and three of these four patients had cancer at sextant biopsy. In the four men with cancer, targeted cores were 5.9 times more likely to be positive (P = .027). Selective suppression of flow in benign tissue was observed in two of the four men with cancer. CONCLUSION: Short-term dutasteride therapy reduces Doppler US flow in the prostate and may improve depiction of hypervascular cancer. RSNA, 2005