Effect of aromatase inhibitors on bone mineral density in a Japanese breast cancer population

We retrospectively analyzed the bone mineral density (BMD) of postmenopausal Japanese women taking an aromatase inhibitor (AI), exemestane, anastrozole or letrozole, and calculated the decrease rate constant of BMD in each individual to compare the influence of the three AIs on BMD. We also aimed to evaluate the preventive effect of bisphosphonates (BPs) on the AI-induced decrease in BMD. The decrease rate constant of BMD (k_e) in each individual was determined as a slope of linear regression of the relationship between time and logarithm of BMD value in each patient during the AI therapy. To compensate for the age-related change in BMD level, we estimated the age-related decrease rate constant of BMD (k_e,0) in healthy Japanese postmenopausal women from the literature. AIs decreased BMD with a k_e value of -0.0329 yr^-1, which was 4.7-fold larger than the k_e,0 value of -0.00699 yr^-1. No significant difference was detected in the influence on BMD among AIs. Co-administration of BP ameliorated the ke value to -0.0117 yr^-1, a value similar to k_e,0. The influence of AIs on BMD was quantitatively evaluated by using the decrease rate constant of BMD (k_e). The present study also suggests that BPs may be useful to prevent the decrease in BMD induced by AIs.