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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 ³.

Principal Investigators

Dr. Paul Goss (Study Chair) and Dr. Kathleen Pritchard, NCIC-Clinical Trials Group ⁴; Dr. James Ingle, NCCTG ⁵; Dr. Matthew Ellis, CALGB ⁶; Dr. George Sledge, ECOG ⁷; Dr. George Budd, SWOG ⁸; and Dr. Manuela Rabaglio, IBCSG ⁹.

Dr. Paul Goss Principal Investigator

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 ¹⁰) 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

This trial is no longer recruiting new patients. To locate other breast cancer clinical trials, search the NCI's database of clinical trials ¹¹ or call the NCI's Cancer Information Service at 1-800-4-CANCER (1-800-422-6237). The call is toll free and completely confidential.

Glossary Terms

An anticancer drug that is used to decrease estrogen production and suppress the growth of tumors that need estrogen to grow. It is a type of nonsteroidal aromatase inhibitor.

A protein found inside the cells of the female reproductive tissue, some other types of tissue, and some cancer cells. The hormone estrogen will bind to the receptors inside the cells and may cause the cells to grow. Also called ER.

A drug used to treat advanced breast cancer and to prevent recurrent breast cancer in postmenopausal women who have already been treated with tamoxifen. It is also being studied in the treatment of other types of cancer. Exemestane causes a decrease in the amount of estrogen made by the body. It is a type of aromatase inhibitor. Also called Aromasin.

An agency in the U.S. federal government whose mission is to protect public health by making sure that food, cosmetics, and nutritional supplements are safe to use and truthfully labeled. The FDA also makes sure that drugs, medical devices, and equipment are safe and effective, and that blood for transfusions and transplant tissue are safe. Also called Food and Drug Administration.

A cell protein that binds a specific hormone. The hormone receptor may be on the surface of the cell or inside the cell. Many changes take place in a cell after a hormone binds to its receptor.

Cancer that has recurred (come back), usually after a period of time during which the cancer could not be detected. The cancer may come back to the same place as the original (primary) tumor or to another place in the body. Also called recurrent cancer.

A problem that occurs when treatment affects healthy tissues or organs. Some common side effects of cancer treatment are fatigue, pain, nausea, vomiting, decreased blood cell counts, hair loss, and mouth sores.

A drug used to treat certain types of breast cancer in women and men. It is also used to prevent breast cancer in women who have had ductal carcinoma in situ (abnormal cells in the ducts of the breast) and in women who are at a high risk of developing breast cancer. Tamoxifen is also being studied in the treatment of other types of cancer. It blocks the effects of the hormone estrogen in the breast. Tamoxifen is a type of antiestrogen. Also called tamoxifen citrate.