Clinical setting overview:

  • Premenopausal: ovarian function intact → need ovarian suppression ± receptor blockade.

  • Postmenopausal: estrogen from peripheral conversion → target aromatase.

  • 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

  • Standard adjuvant: 5 years (AI or tamoxifen).

  • Extended: up to 10 years in high-risk patients (benefit vs bone toxicity).

  • Neoadjuvant: 3–6 months for downstaging ER+ tumors.

Combination strategies

  • CDK4/6 inhibitors (palbociclib / ribociclib / abemaciclib) + AI or SERD → ↑ PFS (~12–15 mo gain).

  • mTOR (everolimus) or PI3K (alpelisib) for resistant disease with matching mutations.

Monitoring

  • Menstrual status, estradiol, FSH if suppression intended.

  • Bone density baseline and q 2 y.

  • Lipids, LFTs q 6 mo.

  • Tumor markers (CA 15-3, CEA) not for routine decision but trend watching.

Key patient guidance

  • Inform about hot flushes, arthralgia, vaginal dryness — manageable with SSRIs or lubricants.

  • Dental precautions if on bisphosphonates / denosumab.

  • Fertility discussion before ovarian suppression.

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