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BACKGROUND	Treatment of breast cancer with aromatase inhibitors is associated with damage to bones .
BACKGROUND	NCIC CTG MA .27 was an open-label , phase 3 , randomised controlled trial in which women with breast cancer were assigned to one of two adjuvant oral aromatase inhibitors-exemestane or anastrozole .
BACKGROUND	We postulated that exemestane-a mildly androgenic steroid-might have a less detrimental effect on bone than non-steroidal anastrozole .
BACKGROUND	In this companion study to MA .27 , we compared changes in bone mineral density ( BMD ) in the lumbar spine and total hip between patients treated with exemestane and patients treated with anastrozole .
METHODS	In MA .27 , postmenopausal women with early stage hormone ( oestrogen ) receptor-positive invasive breast cancer were randomly assigned to exemestane 25 mg versus anastrozole 1 mg , daily .
METHODS	MA .27 B recruited two groups of women from MA .27 : those with BMD T-scores of -20 or more ( up to 2 SDs below sex-matched , young adult mean ) and those with at least one T-score ( hip or spine ) less than -20 .
METHODS	Both groups received vitamin D and calcium ; those with baseline T-scores of less than -20 also received bisphosphonates .
METHODS	The primary endpoints were percent change of BMD at 2 years in lumbar spine and total hip for both groups .
METHODS	We analysed patients according to which aromatase inhibitor and T-score groups they were allocated to but BMD assessments ceased if patients deviated from protocol .
METHODS	This study is registered with ClinicalTrials.gov , NCT00354302 .
RESULTS	Between April 24 , 2006 , and May 30 , 2008 , 300 patients with baseline T-scores of -20 or more were accrued ( 147 allocated exemestane , 153 anastrozole ) ; and 197 patients with baseline T-scores of less than -20 ( 101 exemestane , 96 anastrozole ) .
RESULTS	For patients with T-scores greater than -20 at baseline , mean change of bone mineral density in the spine at 2 years did not differ significantly between patients taking exemestane and patients taking anastrozole ( -092 % , 95 % CI -235 to 050 vs -239 % , 95 % CI -377 to -101 ; p = 008 ) .
RESULTS	Respective mean loss in the hip was -193 % ( 95 % CI -293 to -093 ) versus -271 % ( 95 % CI -432 to -111 ; p = 010 ) .
RESULTS	Likewise for those who started with T-scores of less than -20 , mean change of spine bone mineral density at 2 years did not differ significantly between the exemestane and anastrozole treatment groups ( 211 % , 95 % CI -084 to 506 vs 372 % , 95 % CI 154 to 589 ; p = 026 ) , nor did hip bone mineral density ( 209 % , 95 % CI -145 to 563 vs 00 % , 95 % CI -367 to 366 ; p = 028 ) .
RESULTS	Patients with baseline T-score of -20 or more taking exemestane had two fragility fractures and two other fractures , those taking anastrozole had three fragility fractures and five other fractures .
RESULTS	For patients who had baseline T-scores of less than -20 taking exemestane , one had a fragility fracture and four had other fractures , whereas those taking anastrozole had five fragility fractures and one other fracture .
CONCLUSIONS	Our results demonstrate that adjuvant treatment with aromatase inhibitors can be considered for breast cancer patients who have T-scores less than -20 .
BACKGROUND	Canadian Cancer Society Research Institute , Pfizer , Canadian Institutes of Health Research .

