Postmenopausal Women at Risk for Breast Cancer Experience Negligible Bone Loss With Exemestane: Presented at SABCS
By Jill Stein
SAN ANTONIO -- December 12, 2011 -- Exemestane is associated with a clinically insignificant decline in bone mineral density (BMD) in the hip and spine after 2 years of treatment among postmenopausal women at increased risk of breast cancer, researchers said here December 9 at the 34th Annual San Antonio Breast Cancer Symposium (SABCS).
Paul Goss, MD, Massachusetts General Hospital, Boston, Massachusetts, and colleagues determined differences in hip and spine BMD at 2 years using a noninferiority design in women with a T score higher than -2.0 within 12 months prior to randomisation. A T score higher than -2.0 is better than 2 standard deviations below the average peak BMD of a young adult woman.
Their study, known as MAP3B, was a substudy of the MAP3 trial. The MAP3 study showed that exemestane significantly reduced invasive and pre-invasive breast cancer in postmenopausal women at increased risk for breast cancer trial with no serious toxicities, including excess fractures or osteoporosis.
The MAP3B substudy recruited 238 postmenopausal women who had a median age of 61.8 years.
The analysis showed that the mean percentage change of BMD at 24 months from baseline was -1.8% and -0.46% in the total hip and -1.7% and 0.56% in the L1-L4 posterior-to-anterior (PA) spine for women in the exemestane and placebo arms, respectively.
The upper limit of a 1-side 95% confidence interval (CI) for the difference in mean percentage changes between placebo and exemestane was 2.55% in the total hip and 3.62% in the L1-L4 PA spine.
There were no women in either treatment group who had osteoporosis (T score < -2.5) in either the total hip or L1-L4 spine at 24 months. There were 7 women on exemestane and 2 women on placebo with at least 1 clinical skeletal fracture during treatment (P =.177), 1 of which was a fragility fracture in the exemestane arm.
Dr. Goss said that the observed difference between exemestane and placebo is within the margin of noninferiority although his group cannot conclude that exemestane doesn’t induce significant bone loss in L1-L4 because of the upper limits of the 95% CI for absolute differences between the arms at 24 months. The differences in clinical and fragility fractures were not significant.
He added that study limitations include the small sample size and insufficient power to assess changes in BMD at 24 months.
Funding for this study was provided by Pfizer.
[Presentation title: Influence of Two Years of Exemestane on Bone Mineral Density in Postmenopausal Women at Increased Risk of Developing Breast Cancer; A Companion Study to the NCIC CTG MAP.3 Trial. Abstract P4-11-13]
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