How Exemestane (Aromasin) Works

Exemestane is a type of hormone therapy drug included in the group of aromatase inhibitor drugs, and defined by the National Cancer Institute (NCI) Drug Dictionary as a “synthetic androgen analogue” that “binds irreversibly to and inhibits the enzyme aromatase, thereby blocking the conversion of cholesterol to pregnenolone and the peripheral aromatization of androgenic precursors into estrogens.”

The drug is used for the treatment of breast cancer and it is usually taken in the form of tablets once a day after a meal over the course of a few years. The mechanism of action of exemestane is based on addressing the hormones that stimulate breast cancer growth.

In menstruating women the growth of breast cancer is promoted by female sex hormones called estrogen and progesterone, which are produced in the ovaries. In menopausal women the production of these hormones no longer occur in the ovaries. After menopause, hormones are mainly produced through a process that transform androgens — sex hormones produced by the adrenal glands — into estrogen. This transformation is called aromatase. Exemestane works by blocking aromatase in order to decrease the levels of estrogen in the body and stop cancer growth or breast cancer recurrence.

Exemestane (Aromasin) for Breast Cancer

Exemestane was approved by the U.S. FDA in October 2005. The drug is commercialized under the brand name Aromasin by Pfizer, and is used as an adjuvant treatment in postmenopausal women who suffer from estrogen receptor positive early-stage breast cancer. Women generally begin taking exemestane after they’ve been on tamoxifen for two to three years, then switch to exemestane for two to three years, for a total of five consecutive years of adjuvant hormonal therapy.

The FDA’s approval of the drug was based on a double-blind, multi-center, international clinical trial that included 4,724 postmenopausal women with early stage breast cancer, known as the Intergroup Exemestane Study (IES).

“After a median duration of randomized therapy of 27 months and with a median duration of follow-up of 34.5 months, DFS [disease-free survival] was significantly improved in patients who switched to exemestane compared to those who continued tamoxifen,” according to the NCI. “In the hormone receptor-positive subpopulation representing about 85 percent of the trial patients, DFS was significantly improved in the exemestane arm compared to the tamoxifen arm.”

The same study indicated that the most common side effects from the treatment include hot flashes, fatigue, joint pain, headache, insomnia, increased sweating, hypertension, and dizziness. More rare adverse events, such as heart problems, can also occur.

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