Changes in body composition in women with breast cancer on aromatase inhibitors: A two-year trial
9528 Background: Aromatase inhibitors (AIs), the preferred adjuvant therapy of postmenopausal breast cancer patients, induce severe hypo-estrogenemia which differentiates them from the Estrogen-Receptor-Agonists-Antagonists (ERAAs). Little is known about the effect of AIs on body composition. We sought to examine the impact of AIs on body composition, and whether any changes correlate with gonadal hormone levels. Methods: We analyzed a two year double-blind trial (Risedronate's Effect on Bone loss in Breast CAncer, REBBeCA). 81 chemotherapy-induced newly postmenopausal nonmetastatic breast cancer patients had been randomized to risedronate 35 mg once weekly or placebo and followed, some of whom were on or started AI during the trial. Measures included body composition by whole body DXA-scan and serum sex hormone levels. Combining the two treatment arms, we estimated and compared body composition changes in those on (AI) and not on AIs (no-AI) using a linear mixed model, and examined correlations with serum hormone levels. Results: By 24 months, 41 women were on an AI. Over 2 years, lean mass increased by 1159g (p=0.0003) in women on an AI and did not change (85g; p=0.7684) in the no-AI group (adjusted difference, AD=1047g; p=0.0004). Percent fat did not change (0.0; p=0.9344) in those on an AI and increased (1.2; p=0.0097) in the no-AI group (AD=1.6; p=0.0433). The change in estradiol was associated with changes in lean mass (correlation r=0.42, p=0.0020) and percent fat (r=-0.48, p=0.0003). Conclusions: The use of AIs is associated with a decrease in fat mass and an increase in lean mass. The changes in estradiol are associated with alterations in body composition. The mechanisms and implications of these changes need to be studied further. [Table: see text]