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Title: Exemestane in Treatment of Early Breast Cancer Leads to Significant Decrease in Bone Mineral Density: Presented at ASCO

"Exemestane in Treatment of Early Breast Cancer Leads to Significant Decrease in Bone Mineral Density: Presented at ASCO"

By Cameron E. Johnston ORLANDO, FL -- May 20, 2005 -- Women with early-stage breast cancer who are being treated with the aromatase inhibitor exemestane appear to experience significantly greater losses in bone mineral density (BMD) over a 1-year period than do women who are treated with tamoxifen. This finding could mean that more women who are treated with exemestane are at risk of developing osteoporosis or having bone fractures as their treatment continues than are women who are treated with tamoxifen. Stephen Jones, MD, oncologist, Baylor-Sammons Cancer Center, Dallas, Texas, presented the findings here on May 16[^th at the American Society of Cancer Oncology Annual Meeting (ASCO).

A certain decrease in BMD is to be expected among postmenopausal women, Dr. Jones said, typically in the order of 1% to 2% per year. However, women who have had breast cancer and are receiving tamoxifen show a much smaller loss in BMD, owing to tamoxifen's protective effect on the skeleton. Women who are treated with aromatase inhibitors do not have the same benefit, he said.

In an ongoing trial involving 538 women with early-stage breast cancer, 235 have now completed 1 year of treatment with either tamoxifen 20 mg/day or exemestane 25 mg/day. BMD was measured at baseline and again at the end of the first year.

At the spine, average BMD was 1.10 g/cm² in the tamoxifen group and 1.09 g/cm² in the exemestane group. BMD at the hip was 0.91 g/cm² in both groups.

After 1 year of treatment, there was a decrease in BMD of 3% at the spine and 1% at the hip among women on exemestane. By comparison BMD increased by 1% at the spine and by 3% at the hip in women on tamoxifen. This translates into mean changes in T scores of -0.24 at the spine and -0.25 at the hip between the 2 groups.

The difference in hip T scores was statistically significant; the difference in spine measurements was not.

While more women receiving exemestane already had osteoporosis at baseline, the 4% who had normal BMD at baseline became osteoporotic during the first year, Dr. Jones said. Among women on tamoxifen, 1% became osteoporotic after 1 year.

Similarly, 3% of women who had osteopenia at baseline and were treated with exemestane developed osteoporosis during the first year, compared to 1% of women receiving tamoxifen.

Dr. Jones noted that there were more new fractures in the tamoxifen group during the first year than in the exemestane group.

These findings are not unique to exemestane and appear to be a class effect that is seen with all aromatase inhibitors, Dr. Jones said. This suggests that women who are being treated with these agents should consider bone-strengthening supplements at the very least during the first year of hormonal therapy.

The study is continuing and further yearly measurements of bone mineral density are planned, Dr. Jones said.

[Presentation title: The Effect of Tamoxifen (T) or Exemestane (E) on Bone Mineral Density (BMD) After 1 Year of Adjuvant Treatment of Postmenopausal Women With Early Breast Cancer. Abstract 610]

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