Study strengths and limitations
The authors noted that this updated analysis of the IBIS-II trial data offers further support for the use of anastrozole in breast cancer prevention for high-risk postmenopausal women. The extended posttreatment follow-up showed a significant continuing reduction in breast cancer, and there was no evidence of new late adverse effects. A limitation of the analysis, however, is that very few deaths from breast cancer occurred during the study timeframe. Thus, additional follow-up would be needed to assess anastrozole’s effect on breast cancer mortality.
WHAT THIS EVIDENCE MEANS FOR PRACTICE
The breast cancer chemoprophylactic efficacy of anastrozole compares favorably with that of tamoxifen. Furthermore, in women with an intact uterus, the increased risks of gynecologic problems, including endometrial cancer, associated with tamoxifen do not occur with aromatase inhibitors. However, the lack of any obvious mortality benefit means the ultimate value of estrogen deprivation breast cancer chemoprophylaxis continues to be uncertain, especially given other risks, including bone loss. In view of these new data, it will be important for high-risk women considering aromatase inhibitor prophylaxis to understand that these medications have not been associated with a mortality benefit.
ANDREW M. KAUNITZ, MD, NCMP