No Difference in Bone Mineral Density Changes With Adjuvant Exemestane vs Anastrozole in Women With Early Breast Cancer
In a companion study (MA.27B) to the open-label phase III National Cancer Institute of Canada Clinical Trials Group (NCIC CTG) MA.27 trial in women with early breast cancer reported in The Lancet Oncology, Goss et al found that adjuvant aromatase inhibitor treatment with exemestane, a mildly androgenic steroid, was not associated with less loss of bone mineral density than treatment with the nonsteroidal aromatase inhibitor anastrozole in patients with baseline T-scores ≥ −2. No significant differences in bone mineral density changes were observed in patients with T-scores < −2.
Study Details
In MA.27, postmenopausal women with early-stage hormone receptor–positive invasive breast cancer were randomly assigned to receive oral exemestane 25 mg or oral anastrozole 1 mg daily. The companion MA.27B study recruited two groups of patients from MA.27, consisting of 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.
Between April 2006 and May 2008, 147 exemestane recipients and 153 anastrozole recipients with baseline T-scores of ≥ −2.0 and 101 exemestane patients and 96 anastrozole patients with baseline T-scores < −2.0 were accrued.
No Differences in Bone Mineral Density Change
Among the 300 patients with baseline T-scores ≥ −2.0, there was no significant difference between the exemestane and anastrozole groups in relative mean change in spine bone mineral density (−0.92% vs −2.39%, P = .08) or hip bone mineral density (−1.93% vs −2.71%, P = .10) at 2 years.
Similarly, among the 197 patients with baseline T-scores < −2.0, there was no significant difference between the exemestane and anastrozole groups in relative mean change in spine bone mineral density (2.11% vs 3.72%, P = .26) or hip bone mineral density (2.09% vs 0.0%, P = .28) at 2 years.
Among patients with baseline T-scores ≥ −2.0, fragility fractures occurred in two exemestane patients and three anastrozole patients and other fractures occurred in two and five patients, respectively. Among those with baseline T-scores < −2.0, fragility fractures occurred in one exemestane patient and five anastrozole patients and other fractures occurred in four patients and one patient, respectively.
The investigators concluded, “Our results demonstrate that adjuvant treatment with aromatase inhibitors can be considered for breast cancer patients who have T-scores less than −2.0.”
Paul E. Goss, MD, of Massachusetts General Hospital, is the corresponding author for The Lancet Oncology article.
The study was supported by the Canadian Cancer Society Research Institute, Canadian Institutes of Health Research, and Pfizer. One of the authors, Vered Stearns, MD, has received funding from Novartis and Pfizer.
The content in this post has not been reviewed by the American Society of Clinical Oncology, Inc. (ASCO®) and does not necessarily reflect the ideas and opinions of ASCO®.
