Which Aromatase Inhibitor Has the Edge in Early Breast Cancer?

Lidia Schapira, MD


April 26, 2013

Exemestane Versus Anastrazole in Postmenopausal Women With Early Breast Cancer: NCIC CTG MA.27 -- A Randomized Controlled Phase III Trial

Goss PE, Ingle JN, Pritchard KI, et al
J Clin Oncol. 2013;31:1398-1404

Study Summary

In patients with hormone-dependent postmenopausal breast cancer, standard adjuvant therapy involves 5 years of aromatase inhibition, typically with anastrazole or letrozole. The nonsteroidal aromatase inhibitor exemestane could prove to spare bone and may be another option for treatment.

Goss and colleagues designed an open-label, phase 3, randomized controlled trial of 5 years of exemestane vs anastrozole. The primary objective was disease-free survival; secondary objectives included overall survival, safety, distant disease-free survival, and incidence of contralateral new breast cancers.

The MA.27 study began accrual in 2003 and accrued over 7000 women. All were postmenopausal and had early breast cancer. Of the enrolled patients, 72% had T1 tumors and 71% were node-negative. A minority of women (11%) received bisphosphonate therapy. Approximately 25% were HER2 positive, but the majority of these patients did not receive trastuzumab or other treatment directed against HER2.

Women were randomly assigned to receive either anastrazole or exemestane. Nearly one third (32%) of patients discontinued treatment because of side effects. At a median follow-up of 4.1 years, disease-free survival was excellent and identical among the compared groups at 91%. Patients taking exemestane had less bone loss.

This comparison of steroidal and nonsteroidal aromatase inhibitors showed identical outcomes but less bone toxicity for those taking exemestane. The investigators concluded that exemestane should be considered another option for adjuvant therapy for postmenopausal women with endocrine-sensitive breast cancer.


The role of adjuvant endocrine therapy for women with hormone-sensitive breast cancer is now firmly established. We are still debating the exact duration of therapy and will continue to revise our practice guidelines as new data emerge from trials. These published results from the MA.27 allow us to expand our list of available endocrine options to include exemestane.

We now have 3 US Food and Drug Administration-approved aromatase inhibitors in the United States, and all are available as generic medications. Our current challenge is to understand differences in side-effect profiles and tolerability in order to provide personalized recommendations for treatment. With publication of this study, I think we can consider exemestane as front-line adjuvant therapy for postmenopausal women with endocrine-sensitive breast cancer and poor bone density or those already diagnosed with osteoporosis who are receiving treatment with bisphosphonates.