Steroidal aromatase inhibitors
ATC code: L02BG06 (Exemestane)
Brand names
Aromasin, Exemestano Cinfa, Exemestano Desgen
Irreversible third-generation steroidal aromatase inhibitor. Blocks the aromatase enzyme (CYP19) that converts androgens (testosterone, androstenedione) into estrogens (estradiol, estrone) in peripheral tissues – fat, muscle, tumor. In postmenopausal women this peripheral pathway becomes the main estrogen source after ovarian function ceases. Unlike reversible non-steroidal inhibitors (anastrozole, letrozole), exemestane binds aromatase irreversibly.
First line
Adjuvant therapy of early ER+ breast cancer in postmenopausal women and treatment of metastatic disease. Per ESMO 2024 and Spanish SEOM 2023 exemestane is used as first-line or as a switch after 2-3 years of tamoxifen (TEAM, BIG 1-98). Dose 25 mg once daily after meals. Adjuvant duration – 5 years (with or without tamoxifen). In metastatic disease – until progression with switch to letrozole or fulvestrant. Alternatives – anastrozole, letrozole.
The drug is promoted for these uses outside international guidelines. Each entry below is analyzed against AEMPS, FDA, EMA, Cochrane and major RCTs.
Not recommended
Exemestane is used by amateur bodybuilders and AAS users as a steroidal aromatase inhibitor. ASCO 2022 and the AEMPS Ficha Técnica confine exemestane to hormone-receptor-positive breast cancer in postmenopausal women. Approved indications in male athletes do not exist. Use causes marked bone mineral density loss, arthralgia, hypertension and psychiatric effects.
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Contraindicated in pregnancy. For premenopausal breast cancer – tamoxifen with ovarian suppression. In women with conception potential, contraception is mandatory.
Contraindicated during lactation.
Reference information, not a clinical decision. Discuss feeding pauses or changes with your physician or an IBCLC.
Exemestane is evaluated for the following indications with varying evidence strength: ER-positive breast cancer (evidence tier A), Athletic endurance (evidence tier F). See the full indication matrix with dosing and citations above on this page.
Common side effects of Exemestane (≥ 1 in 100): Hot flashes, Joint pain, Fatigue, Insomnia, Sweating, BMD reduction. See the Safety section for uncommon and serious reactions.
FDA category X. Contraindicated in pregnancy. For premenopausal breast cancer – tamoxifen with ovarian suppression. In women with conception potential, contraception is mandatory.
Contraindicated during lactation.
Exemestane is contraindicated in: Hypersensitivity; Pre- and perimenopausal status; Pregnancy and lactation; Severe hepatic or renal impairment. Full list in the Safety section.