Objectives. To determine whether baseline prostate-specific antigen (PSA), in addition to prostate volume, is associated with long-term changes in symptoms and urinary flow rate.

Methods. Three thousand forty men with benign prostatic hyperplasia enrolled in the PLESS trial were randomly assigned to finasteride 5 mg or placebo for 4 years. Symptoms and flow rate were assessed every 4 months, and data were analyzed by dividing the patients into three groups by baseline PSA tertiles (0 to 1.3, 1.4 to 3.2, and 3.3 ng/mL or greater) and baseline prostate volume tertiles (14 to 41, 42 to 57, and 58 to 150 mL).

Results. After the initial placebo effect, a slow deterioration in symptoms over time was observed in the placebo-treated men with a baseline PSA 1.4 ng/mL or greater. However, placebo-treated men in the lowest PSA tertile (less than 1.4 ng/mL) had sustained symptomatic improvement that was not seen in placebo-treated men in the higher tertiles (P <0.001). In all finasteride-treated groups, there was initial improvement followed by maintenance or continued symptom improvement over time (3 to 3.5 points by the end of 4 years). The differences in symptom score improvement between placebo and finasteride were marginal for men with baseline PSA levels less than 1.4 ng/mL (P = 0.128) but were highly significant for men with PSA levels 1.4 ng/mL or greater (P <0.001). Urinary flow rate results were similar to those observed for symptoms. Analysis of symptom and flow rate data by prostate volume tertiles in a 10% subset of men yielded similar results, namely a deterioration of symptoms and flow rate in the two higher tertiles treated with placebo (greater than 41 mL) and a sustained improvement in all three groups of finasteride-treated patients.

Conclusions. Baseline PSA and prostate volume are good predictors of long-term symptomatic and flow rate changes. Baseline PSA levels of 1.4 ng/mL or greater and enlarged prostate glands predict the best long-term response to finasteride compared with placebo.