Clinical setting overview:
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Premenopausal: ovarian function intact → need ovarian suppression ± receptor blockade.
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Postmenopausal: estrogen from peripheral conversion → target aromatase.
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Endocrine therapy is first-line for ER/PR-positive, HER2-negative disease (unless visceral crisis).
(NCCN Breast 2025; ESMO Breast 2024)
Main drug classes & regimens
| Class | Mechanism | Examples (Trade) | Typical Dose / Route | Comments |
|---|---|---|---|---|
| Selective Estrogen Receptor Modulator (SERM) | ER antagonist in breast, agonist in bone / endometrium | Tamoxifen (Nolvadex®) | 20 mg PO daily | Adjuvant × 5 y (premenopausal or post-menopause intolerant to AI); ↑ VTE risk & endometrial cancer |
| Aromatase Inhibitors (AI) | Inhibit CYP19A1 → ↓ estrogen synthesis (post-menopause) | Anastrozole (Arimidex®), Letrozole (Femara®), Exemestane (Aromasin®) | 1 mg / 2.5 mg / 25 mg PO daily | First-line postmenopausal; bone loss → DEXA monitor; arthralgia common |
| Selective Estrogen Receptor Degrader (SERD) | ER degradation | Fulvestrant (Faslodex®) | 500 mg IM D0, 14, 28 → q28d | Used after AI failure or ESR1 mutation |
| Ovarian Suppression | Gonadotropin-releasing hormone (GnRH) agonists ↓ LH/FSH | Goserelin (Zoladex®) 3.6 mg SC q4wk / 10.8 mg q12wk Leuprolide (Lucrin®) 3.75 mg IM q4wk | Combine with AI or tamoxifen in premenopausal patients |
Duration
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Standard adjuvant: 5 years (AI or tamoxifen).
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Extended: up to 10 years in high-risk patients (benefit vs bone toxicity).
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Neoadjuvant: 3–6 months for downstaging ER+ tumors.
Combination strategies
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CDK4/6 inhibitors (palbociclib / ribociclib / abemaciclib) + AI or SERD → ↑ PFS (~12–15 mo gain).
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mTOR (everolimus) or PI3K (alpelisib) for resistant disease with matching mutations.
Monitoring
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Menstrual status, estradiol, FSH if suppression intended.
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Bone density baseline and q 2 y.
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Lipids, LFTs q 6 mo.
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Tumor markers (CA 15-3, CEA) not for routine decision but trend watching.
Key patient guidance
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Inform about hot flushes, arthralgia, vaginal dryness — manageable with SSRIs or lubricants.
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Dental precautions if on bisphosphonates / denosumab.
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Fertility discussion before ovarian suppression.