Exemestane belongs to a class of drugs called aromatase inactivators. These medications are responsible for decreasing circulating estrogen, and affect cancer by acting on breast cancer cells that may be estrogen dependent. Exemestane is a selective treatment for some postmenopausal women with hormone dependent breast cancer. The medication is for postmenopausal women with advanced breast cancer whose disease has progressed following tamoxifen therapy.

Aromatase inhibition is a method of controlling breast cancer cell growth, in cases where the cancer cells have grown resistant to tamoxifen. Aromatase inhibitors may be poised to take the place of tamoxifen. As their name implies, these compounds inhibit aromatase, an enzyme that helps make estrogen. Exemestane is actually slightly different from the other two medications in that it has a "steroidal structure."

Exemestane is a hormonal drug that prevents the growth of breast cancer by inhibiting the enzyme aromatase, which is involved in the production of estrogen. Exemestane significantly lowers the amount of estrogen in post-menopausal women by inhibiting the conversion of androgens (made in the adrenal glands) to estrogen. Exemestane is one of a new group of drugs called the aromatase inhibitors. They bind to an enzyme involved in estrogen production in the breast. Their role in breast cancer is, like the more well-known drug tamoxifen, to block the action of estrogen in tumors that are otherwise stimulated by it. But aromatase inhibitors act on a different part of the pathway.

Exemestane is the only aromatase inactivator and works by irreversibly binding to the protein aromatase, which ultimately blocks the entire conversion process that is responsible for creating the active form of estrogen. This reduces levels of the active form of estrogen in the body, so that cancer cells are depleted of necessary growth stimulant. Exemestane has already been approved by the Federal Drug Administration (FDA) for use in post-menopausal breast cancer patients who have stopped responding to tamoxifen. Results of one of several trials evaluating exemestane as initial treatment for women with advanced estrogen receptor-positive breast cancer were recently reported.