The effect of dutasteride on the peripheral and transition zones of the prostate and the value of the transition zone index in predicting treatment response

PURPOSE: We determined the effects of dutasteride on transition and peripheral zone volume, and the clinical value of the transition zone index in men with benign prostatic hyperplasia. MATERIALS AND METHODS: A total of 2,802 men 50 years or older with diagnosed benign prostatic hyperplasia, American Urological Association symptom index score 12 or greater, total prostate volume 30 cc or greater, prostate specific antigen 1.5 ng/ml or greater and 10 ng/ml or less, and peak urinary flow rate 15 ml per second or less were randomized to receive 0.5 mg dutasteride daily or placebo for 2 years. Total prostate and transition zone volume was measured with transrectal ultrasound at baseline and 4 times during the 2-year period. Peripheral zone volume (total prostate volume minus transition zone volume) and the transition zone index (transition zone volume/total prostate volume) were calculated. Patients were stratified into tertiles according to baseline total prostate and transition zone volume, and the transition zone index. RESULTS: At 24 months dutasteride significantly decreased total prostate volume from baseline (p <0.0001). There were similar decreases in transition and peripheral zone volume (approximately 25%). In men receiving placebo high baseline total prostate and transition zone volume, and transition zone index were associated with poor 2-year outcomes, ie a low peak urinary flow rate, high American Urological Association symptom index scores, and an increased frequency of acute urinary retention and benign prostatic hyperplasia related surgery. Improvements in outcomes with dutasteride vs placebo were greatest in men with the highest baseline total prostate and transition zone volume, and transition zone index. In men with low (30 to less than 42 cc) and intermediate (42 to less than 58 cc) baseline total prostate volume the benefits of dutasteride therapy were only significant in the intermediate (0.4 to less than 0.55) and high (0.55 to less than 1.0) transition zone index tertiles. CONCLUSIONS: Total prostate and transition zone volume, and the transition zone index are directly related to benign prostatic hyperplasia progression. The transition zone index may add value to transition zone volume alone for predicting outcomes. Dutasteride decreased transition and peripheral zone volume equally, supporting a known therapeutic role in benign prostatic hyperplasia and a possible preventive role in prostate cancer.