What Is Exemestane (Aromasin)? FDA Approval, Licensing in Türkiye and Reimbursement Status
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Irreversible Blockade in Hormone-Sensitive Breast Cancer: Exemestane
Used in breast cancer treatment, Exemestane (Aromasin®)is a steroidal agent that, unlike other aromatase inhibitors, binds to the enzyme “irreversibly.” Particularly in postmenopausal women, it permanently stops estrogen synthesis, cutting off cancer cells’ growth signals and minimizing recurrence risk.
Drug Profile
- Brand Name: Aromasin® (and equivalents)
- Active Ingredient: Exemestane
- Class: Steroidal Aromatase Inhibitor (Type I)
- Administration: Oral Tablet (By mouth)
- Manufacturer: Pfizer
- License: Licensed in Türkiye.
- Payment: Included in the SGK reimbursement list (SUT).
- Reimbursement Conditions: For postmenopausal patients with hormone receptor-positive breast cancer, in the neoadjuvant, adjuvant or metastatic setting, based on a specialist medical report, the cost is reimbursed.
- Price: For 30 Tablets of 25 mg, approximately 750 - 950 TL (current pharmacy retail prices may vary).
Approved Indications
- Adjuvant Treatment (Switch Therapy): For postmenopausal women who have taken Tamoxifen for 2-3 years, to complete a total of 5 years of hormonal therapy.
- Advanced Breast Cancer: In patients with progression after Tamoxifen or other hormonal therapies.
- Combination Therapy: With targeted agents such as Everolimus in certain situations (metastatic disease).
Clinical Importance and History
Exemestane’s efficacy was established in a large trial that changed treatment protocols:
The trial showed that patients who switched to Exemestane after 2-3 years of Tamoxifen had a much lower recurrence risk and higher survival than those receiving Tamoxifen alone for 5 years. This strategy is called “Sequential (Switch) Therapy.”
What Is Exemestane? Its Molecular Mechanism of Action
Exemestane is a steroidal molecule whose structure resembles the body’s natural androgens (androstenedione). The main distinction from drugs such as Anastrozole is that it produces "Suicide Inhibition" (irreversible enzyme inhibition).
🔬 How It Works at the Molecular Level
The aromatase enzyme is the main site responsible for estrogen production after menopause. Exemestane intervenes in this process as follows:
- 1. Irreversible Binding (Suicide Inhibitor): Exemestane enters the aromatase enzyme’s active site like a false key and forms a covalent (permanent) bond. The enzyme can no longer function, and the blockade continues until the body produces new enzyme.
- 2. Advantage of a Steroidal Structure: Its steroidal structure means it may remain effective in cells that have developed resistance to some other aromatase inhibitors.
- 3. Maximum Suppression: Daily dosing lowers blood estrogen levels by approximately 90-95%, completely cutting off cancer cells’ nourishment.
Administration and Dosage
Timing matters because food increases Exemestane absorption:
- Standard Dose: A 25 mg tablet once daily.
- Administration: To maximize absorption, the medicine should preferably be taken after meals each day.
- Duration: According to the physician’s protocol, usually during a 2-3-year “switch” period or for the full 5-year course.
Side Effects and Management
Side effects usually result from estrogen deficiency, but its steroidal structure may produce some differences:
- Joint and Bone Pain: Occurs in approximately 15-20% of patients. Light exercise and calcium supplementation are recommended.
- Hot Flashes and Sweating: Among the most common complaints (14%).
- Osteoporosis Risk: May reduce bone mineral density. Regular DEXA monitoring is needed.
- Insomnia and Fatigue: Some patients may experience disturbed sleep patterns.
- Digestive Problems: May rarely cause nausea or abdominal pain; taking it with food reduces this risk.
Special Situations and Warnings
- Menopausal Status: Effective only in postmenopausal women. Contraindicated in menstruating women because it may overstimulate the ovaries.
- Vitamin D Monitoring: Vitamin D deficiency may be more common in patients taking Exemestane, so supplementation is generally needed.
- Athletes and Doping: Its steroidal structure may place it on prohibited substance lists in sports competitions because it alters the testosterone/estrogen balance.
References
- FDA Approved Labeling for Aromasin (exemestane) tablets.
- Coombes RC, et al. A randomized trial of exemestane after two to three years of tamoxifen therapy (IES). N Engl J Med. 2004.
- Paridaens RJ, et al. Exemestane vs tamoxifen as first-line therapy (EORTC 10951). J Clin Oncol. 2008.
- T.C. Sağlık Bakanlığı, Aromasin 25 mg Kısa Ürün Bilgisi (KÜB).
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