Last reviewed 2026-04-20 · How we verify

Aromasin (exemestane)

Aromasin works by blocking the aromatase enzyme, which is responsible for converting androgens into estrogens.

Aromasin (exemestane) is a small molecule aromatase inhibitor developed by Pharmacia and Upjohn, now owned by Pfizer. It targets the aromatase enzyme to reduce estrogen production in the body, making it effective in treating hormone receptor-positive breast cancer that has progressed after anti-estrogen therapy. Aromasin is FDA-approved for advanced breast cancer and is available as a generic medication. With a half-life of 24 hours and bioavailability of 42%, it is a well-established treatment option. As an off-patent medication, Aromasin is widely available from multiple generic manufacturers.

At a glance

Mechanism of action

Breast cancer cell growth may be estrogen-dependent. Aromatase is the principal enzyme that converts androgens to estrogens both in pre- and postmenopausal women. While the main source of estrogen (primarily estradiol) is the ovary in premenopausal women, the principal source of circulating estrogens in postmenopausal women is from conversion of adrenal and ovarian androgens (androstenedione and testosterone) to estrogens (estrone and estradiol) by the aromatase enzyme in peripheral tissues.Exemestane is an irreversible, steroidal aromatase inactivator, structurally related to the natural substrate androstenedione. It acts as false substrate for the aromatase enzyme, and is processed to an intermediate that binds irreversibly to the active site of the enzyme, causing its inactivation, an effect also known as suicide inhibition. Exemestane significantly lowers circulating estrogen concentrations in postmenopausal women, but has no detectable effect on adrenal b

Approved indications

• Advanced Breast Cancer Progression Post-Antiestrogen Therapy
• Hormone receptor positive malignant neoplasm of breast

Common side effects

• Hot flushes
• Arthralgia
• Increased sweating
• Alopecia
• Hypertension
• Insomnia
• Nausea
• Fatigue
• Abdominal pain
• Depression
• Diarrhea
• Dizziness

Key clinical trials

• A Study of Elacestrant Versus Standard Endocrine Therapy in Women and Men With ER+,HER2-, Early Breast Cancer With High Risk of Recurrence (PHASE3)
• Testing Whether Hormone Therapy With Ribociclib is as Effective as Chemotherapy Followed by Hormone Therapy With Ribociclib for the Treatment of High Anatomic Stage Breast Cancer With Low Recurrence Risk, The RxFINE-Low Trial (PHASE3)
• Hormone Therapy With or Without Combination Chemotherapy in Treating Women Who Have Undergone Surgery for Node-Negative Breast Cancer (The TAILORx Trial) (PHASE3)
• A Study of LOXO-783 in Patients With Breast Cancer/Other Solid Tumors (PHASE1)
• Tamoxifen Citrate, Letrozole, Anastrozole, or Exemestane With or Without Chemotherapy in Treating Patients With Invasive RxPONDER Breast Cancer (PHASE3)
• Study of Belzutifan (MK-6482) Plus Fulvestrant for ER+/HER2- Metastatic Breast Cancer (MK-6482-029/LITESPARK-029) (PHASE2)
• Ribociclib And Endocrine Treatment of Physician's Choice for Locoregional Recurrent, Resected Hormone Receptor Positive HER2 Negative Breast Cancer (PHASE2)
• A Study of Tersolisib (LY4064809/STX-478) With Other Anti-Cancer Treatments in Participants With Advanced Breast Cancer With a Genetic Change (PIK3CA) (PHASE3)

Primary sources

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