(ChemotherapyAdvisor) – Despite calcium and vitamin D supplementation, postmenopausal women who take exemestane to prevent breast cancer have significantly worse age-related bone loss, results from a nested substudy of the Mammary Prevention 3 (MAP.3) trial concluded in an article in The Lancet Oncology, published online before in print on February 7.
The National Cancer Institute of Canada primary prevention MAP.3 trial randomized 4,500+ healthy postmenopausal women at high risk of developing breast cancer to exemestane 25mg/day or placebo. Exemestane, a third-generation aromatase inhibitor, reduced the risk of developing breast cancer by 65% vs. placebo.
In the nested substudy to quantify the effect of exemestane on the skeleton, Angela M. Cheung, MD, PhD, of University Health Network, Toronto, Canada, and colleagues examined results from 351 nonosteoporotic postmenopausal women with a median age of 61.3 years who were given exemestane (n=176) or placebo (n=175) and followed for two years. Bone mineral density (BMD) was measured by dual-energy x-ray absorptiometry (DEXA) and high-resolution peripheral quantitative CT.
From baseline to two years, distal radius volumetric BMD loss was significantly greater in the exemestane group (-6.1%) vs. placebo (-1.8%) compared with baseline; distal tibia loss was -5.0% and -1.3%, respectively. Mean percent change in cortical thickness at the distal radius was -7.9% in the exemestane group and -1.1% in the placebo group. Decline in areal BMD, as measured by DEXA, was significantly greater at the lumbar spine, total hip, and femoral neck in the exemestane group vs. placebo.
“Women considering exemestane for the primary prevention of breast cancer should weigh their individual risks and benefits,” the authors stated. “For women taking exemestane, regular bone monitoring plus adequate calcium and vitamin D supplementation are important. Long-term studies are needed to assess the effect of our findings on fracture risk.”