(February 7, 2012 - Insidermedicine)

Bone loss is accelerated among postmenopausal women taking exemestane for the primary prevention of breast cancer, according to research published online ahead of print in The Lancet Oncology.

Here are some recommendations for the use of pharmacological agents for breast cancer risk reduction, from the American Society of Clinical Oncology:

•    Five years of tamoxifen (20 mg/d) may be offered to women at increased risk of breast cancer to reduce their risk of estrogen receptor (ER)–positive invasive breast cancers for up to 10 years

•    Raloxifene (60 mg/d) for 5 years may be offered as another option to reduce the risk of ER-positive invasive breast cancer

•    Aromatase inhibitors are not recommended for use in lowering breast cancer risk outside the investigational setting

Researchers out of the University Health Network in Toronto conducted a nested substudy of the MAP.3 trial, in which patients were randomized to treatment with 25 mg of exemestane daily or placebo for the primary prevention of breast cancer. The participants also took calcium and vitamin D supplements. The substudy involved 351 postmenopausal women who were not osteoporotic, not receiving drugs for bone-related disorders, and who had baseline lumbar spine, total hip, and femoral neck T-scores above -2.0. The investigators looked at changes in total volumetric bone mineral density (BMD) at the distal radius and other sites as measured by high-resolution peripheral quantitative CT over two years.

Among 242 women who completed two years of follow-up, mean percent change in total volumetric BMD at the distal radius was -6.1% among those on exemestane vs. only -1.8% for those on placebo. At the distal tibia, the mean percent change was -5.0% for those on exemestane vs. -1.3% for those on placebo. Mean percent change in cortical thickness was -7.9% in the exemestane group vs. -1.1% in the placebo group at the distal radius and -7.6% vs. 0.7% at the distal tibia. In addition, a significantly greater  decline in areal BMD, at measured by dual energy X-ray absorptiometry, was seen in the exemestane group compared with the placebo group in the lumbar spine, total hip, and femoral neck.

Today’s research demonstrates that exemestane therapy worsens age-related bone loss in postmenopausal women, even when taking in combination with vitamin D and calcium supplements. This should be considered when assessing the risks vs. benefits of taking exemestane. In addition, women who do take the drug should undergo regular bone monitoring and maintain adequate calcium and vitamin D supplementation.