Name of the Trial
Phase III Randomized Adjuvant Study of Exemestane Versus Anastrozole in Postmenopausal Women with Receptor-Positive Primary Breast Cancer (CAN-NCIC-MA27). See the protocol summary at http://cancer.gov/clinicaltrials/CAN-NCIC-MA27.

Principal Investigators
Dr. Paul Goss (Study Chair) and Dr. Kathleen Pritchard, NCIC-Clinical Trials Group; Dr. James Ingle, NCCTG; Dr. Matthew Ellis, CALGB; Dr. George Sledge, ECOG; Dr. George Budd, SWOG; and Dr. Manuela Rabaglio, IBCSG

Why This Trial Is Important
Aromatase inhibitors (AIs) have emerged as an important treatment option for postmenopausal women with hormone receptor-positive breast cancer. AIs interfere with the body's ability to make the hormone estrogen, which can fuel the growth of breast cancer cells that have estrogen receptors. AIs block the activity of an enzyme called aromatase, which is necessary to make estrogen.

Anastrozole (Arimidex) and exemestane (Aromasin) are two AIs approved by the FDA to treat early-stage, hormone receptor-positive breast cancer. Anastrozole is a reversible inhibitor that competes with estrogen precursor molecules for binding to aromatase; exemestane attaches permanently to aromatase, preventing estrogen precursors from binding to the enzyme at all (making it an irreversible "suicide" inhibitor). Exemestane also exerts androgenic (male hormone-like) effects in women, and this may contribute to its anticancer efficacy while possibly causing fewer side effects.

In this clinical trial, postmenopausal women with hormone receptor-positive breast cancer that has been surgically removed will be randomly assigned to receive either anastrozole or exemestane for 5 years. Doctors will monitor breast cancer recurrence and the side effects of these drugs. Separate companion studies will examine whether there is a difference in how the drugs affect bone mineral density and breast density in these patients; only those locations enrolling patients in the breast density companion study (NCCTG-N0434) are currently accepting patients for the AI study.

"While anastrozole and exemestane have not been compared previously in a clinical trial, evidence from preclinical studies and other clinical trials comparing each agent to tamoxifen support the idea that exemestane may be a more potent inhibitor of aromatase and have androgenic effects that may be important in enhancing efficacy and affording a better side effect profile," Dr. Goss said.

For More Information
See the lists of entry criteria and trial contact information at http://cancer.gov/clinicaltrials/CAN-NCIC-MA27 or call the NCI's Cancer Information Service at 1-800-4-CANCER (1-800-422-6237). The toll-free call is confidential.