Abstract

Purpose: Fragility fracture risk in patients with prostate cancer is an important issue. The purpose of this study was to accurately assess the impact of androgen deprivation therapy on lumbar spine bone loss using quantitative computed tomography in a propensity-matched cohort of patients with prostate cancer. Materials and Methods: Eighty-one patients with prostate cancer who underwent androgen deprivation therapy for 1 year were included. Thirty-nine of these patients were successfully propensity-matched with 39 of 68 patients from a control group who underwent robot-assisted radical prostatectomy without androgen deprivation therapy. Volumetric bone mineral density of trabecular bone in each vertebral body (L1-L4) was measured using quantitative computed tomography during staging and at 1 year after commencing treatment. The change in mean lumbar volumetric bone mineral density (L1-L4) was then calculated. Results: Propensity score matching successfully achieved comparable baseline patient characteristics and radiological parameters between the androgen deprivation therapy and control groups. In the androgen deprivation therapy group, the decrease in lumbar volumetric bone mineral density (L1-L4) was significantly greater with confirmed testosterone deficiency (−17.9 ± 12.0%) compared with the control group (−8.5 ± 10.8%, P < .001). Conclusions: This study observed a 17.9% reduction in volumetric lumbar bone mineral density (g/cm 3 ) after 1 year of androgen deprivation therapy, exceeding previously reported values (g/cm 2 ) obtained using dual-energy X-ray absorptiometry. The potential overestimation of lumbar spine bone mineral density measured by dual-energy X-ray absorptiometry in older patients with prostate cancer because of concomitant lumbar degenerative disease is a possible reason for this discrepancy. Androgen deprivation therapy may decrease vertebral bone mass and increase the risk of vertebral fractures more than urologists realize.