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Treatment Options for ER-positive Breast Cancer

September 1, 2011

Written By Michael J. Formica, MS, MA, EdM
Reviewed By Jennifer L.A. Armstrong, MD

Results from a clinical trial presented at the San Antonio Breast Cancer Symposium show that, when compared with anastrozole (Arimidex), exemestane (Aromasin) provided similar treatment benefits for postmenopausal women affected by early-stage, hormone receptor-positive breast cancer. However, participants who took exemestane were less likely to develop osteoporosis and high blood cholesterol.

These findings suggest that exemestane, which is currently FDA approved as a second treatment after two or three years of tamoxifen, might also be used as a primary treatment for hormone-sensitive breast cancer.

Reason for the Study

After menopause, the ovaries stop producing estrogen. At this time, an enzyme called aromatase converts testosterone into estradiol, the form of estrogen found in the body after menopause. Estradiol can contribute to the growth of hormone receptor-positive breast cancers.

Hormone receptor-positive breast cancer is treated with anti-estrogen therapy. Aromatase inhibitors are medicines that block aromatase from converting hormones to estradiol. This study was the first head-to-head comparison of two aromatase inhibitors.

Anastrozole is approved as a first-line, adjuvant, or post-surgery, treatment. Exemestane is an adjunctive, or additional, therapy used after initial first-line, adjuvant hormonal therapy with tamoxifen.

Investigators wanted to compare exemestane to anastrozole as a first-line, adjuvant ER-positive treatment because the medicines work differently. Exemestane permanently blocks aromatase from converting testosterone. Anastrozole only does this temporarily. Researchers wanted to look at whether these differences would produce different outcomes.

Goals of the Study

The primary goal of the study was to examine event-free survival, the number of times participants had a local recurrence. Secondary goals included comparing the groups for overall survival, or how long participants lived since entry into the clinical trial. The researchers also compared the groups for distant recurrence, contralateral breast cancer (occurrence in the other, healthy breast) and side effects.

Study Summary

The study included 7,576 postmenopausal women with hormone receptor-positive breast cancer. About 70 percent had lumpectomy, and 72 percent were diagnosed with Stage I cancer, with a tumor of less than 2 centimeters across and no cancer in the lymph nodes. About a third of the participants had adjuvant chemotherapy.

Participants were randomly assigned to two groups, and each group took a daily anastrozole (1mg/day) or exemestane (25mg/day) pill for five years. Initially, the groups also received either celecoxib (Celebrex) or a placebo, but this part of the trial was discontinued two years into the study because celecoxib caused heart problems in some individuals.

Study Findings

Results showed an event-free survival for both groups of about 96 percent, and an overall survival rate of about 94 percent. Breast cancer-specific survival was about 97 percent for both groups. However, women who took exemestane were less likely to develop osteoporosis or high blood cholesterol.

In an interview following his presentation, Paul E. Goss, MD, PhD, professor of medicine at Harvard Medical School in Boston and the study‚Äôs principal investigator, said exemestane could be considered an alternative to anastrozole as a primary adjuvant therapy. 

What Does This Study Mean for Me?

Exemestane is not yet FDA approved to be given as initial, adjuvant therapy, but these results could prompt changes in the current standard of care.

Consult with your care team if you have any questions, or if you are interested in exploring your eligibility for further clinical trials that may investigate exemestane as a treatment option.

Learn more about this study

Goss PE, Ingle JN, Chapman J-AW, et al: Final analysis of NCIC CTG MA.27: A randomized phase III trial of exemestane versus anastrozole in postmenopausal women with hormone receptor positive primary breast cancer. 33rd Annual San Antonio Breast Cancer Symposium. Abstract S1-1. Presented December 9, 2010.

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