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Fracture Rates Similar Between Tamoxifen and Exemestane: Presented at SABCS

By Ed Susman

SAN ANTONIO, TX -- December 13, 2005 -- Researchers said that fracture rates are similar after 2 years of treatment with tamoxifen or exemestane in the Intergroup Exemestane Study (IES).

Researchers entered 206 women with breast cancer into a substudy of the IES that concentrated on bone markers and fracture rates among study subjects. The women had been on tamoxifen for 2 to 3 years and then were randomized to either switch to exemestane or continue on tamoxifen.

"There were no statistically significant differences between groups in number of patients reporting fractures by 24 months," said Robert Coleman, MD, professor and honorary consultant medical oncologist, Cancer Research Centre, Academic Unit of Clinical Oncology, Weston Park hospital, Sheffield, United Kingdom.

There were 8 fractures in the subprotocol group, Dr. Coleman reported in his poster presentation on December 10^th at the 28^th Annual San Antonio Breast Cancer Symposium (SABCS). Two fractures were traumatic fractures and 6 were caused by frailty. Of those 6, there were 3 in the tamoxifen group (2.8%) and 3 in the exemestane group (3%).

The fracture rates in the substudy followed a similar pattern when compared with the main study. Fracture rates were 4.8% in the exemestane group and 3.9% in the tamoxifen group, Dr. Coleman said. That difference failed to reach statistical significance (P = .120).

Bone markers and bone marrow density changed significantly within 6 months of stopping tamoxifen and starting exemestane, Dr. Coleman said. "This is most likely to be due to rapid cessation of bone turnover suppression by tamoxifen."

He noted that after that period, bone mineral density declines continued at the rate of less than 1% per year. "That is similar to what we would expect to see with other aromatase inhibitors, he added.

"On average, the overall 5-year effects on bone mineral density of tamoxifen followed by exemestane are similar to the expected bone loss in a normal age matched population," he said.


[Presentation title: Skeletal Effect of Exemestane in the Intergroup Exemestane Study (IES) 2 Year Bone Mineral Density (BMD) and Bone Biomarker Data. Abstract 5076]

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