There was no significant difference in bone mineral density loss among women with early breast cancer treated with adjuvant Aromasin® (exemestane) or Arimidex® (anastrozole), according to the results of a study published in The Lancet Oncology.
Aromatase inhibitors are drugs that block the production of estrogen in postmenopausal women. These drugs are commonly used in the treatment of hormone receptor-positive breast cancer, and may also have a role in breast cancer prevention—particularly in women at high risk of the disease.
Although aromatase inhibitors provide benefit, these drugs have also been reported to adversely affect bone—and researchers continue to study how these drugs affect bone mineral density. Some have speculated that Aromasin, a mildly androgenic steroid, may be less detrimental to bone than non-steroidal Arimidex.
MA.27B was a companion study to an open-label phase III study known as MA.27, which included postmenopausal women with early stage hormone receptor-positive invasive breast cancer who were randomly assigned to receive Aromasin or Arimidex. In this companion study, researchers compared changes in bone mineral density (BMD) in the lumbar spine and total hip between patients treated with Aromasin and patients treated with Arimidex.
The companion study included two groups of women from MA.27: 300 patients with bone mineral density T-scores ≥ −2.0 (up to two standard deviations below sex-matched, young adult mean) and 197 with at least one T-score (hip or spine) < −2.0. Both groups received vitamin D and calcium and patients with T-scores < −2.0 received bisphosphonates. The primary endpoints were percent change in bone mineral density at 2 years in lumbar spine and total hip for both groups.
At two years, the results indicated that there was no significant difference between the Aromasin and Arimidex groups in terms of changes in bone mineral density in the spine or hip. This was true regardless of the baseline T-score.
Among patients with baseline T-scores ≥ −2.0, fragility fractures occurred in two Aromasin patients and three Arimidex patients and other fractures occurred in two and five patients, respectively. Among those with baseline T-scores < −2.0, fragility fractures occurred in one Aromasin patient and five Arimidex patients and other fractures occurred in four patients and one patient, respectively.
The researchers concluded that there is no significant difference in bone mineral changes among women treated with Aromasin and Arimidex. They note that their results demonstrate that adjuvant treatment with aromatase inhibitors can be used in patients with T-scores less than −2.0.
Goss PE, Hershman DL, Cheung AM, et al: Effects of adjuvant exemestane versus anastrozole on bone mineral density for women with early breast cancer (MA.27B): a companion analysis of a randomised controlled trial. The Lancet Oncology. Published early online March 11, 2014. doi:10.1016/S1470-2045(14)70035-X
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