Indication
- Used in hormone receptor–positive (ER+ and/or PR+) breast cancer, both early-stage and metastatic.
- Works by reducing estrogen stimulation of tumor cells.
| Class | Drug(s) | Mechanism | Indication | Key Adverse Effects | Pharmacist Notes |
|---|---|---|---|---|---|
| SERM (Selective Estrogen Receptor Modulator) | Tamoxifen | Blocks estrogen receptors in breast tissue; partial agonist in bone/endometrium | Premenopausal & postmenopausal; adjuvant, metastatic, risk reduction | Hot flashes, vaginal discharge, thromboembolism, ↑ risk of endometrial cancer | Avoid strong CYP2D6 inhibitors (e.g., paroxetine, fluoxetine); monitor for VTE; ophthalmic exam if long-term use |
| Aromatase Inhibitors (AIs) | Anastrozole, Letrozole (nonsteroidal); Exemestane (steroidal) | Inhibit aromatase → ↓ peripheral conversion of androgens to estrogen | Postmenopausal (or premenopausal with OFS); adjuvant or metastatic | Arthralgias, bone loss, hot flashes, fatigue | Bone density monitoring; Ca/Vit D supplementation; Exemestane may be preferred after nonsteroidal AI resistance |
| SERD (Selective Estrogen Receptor Degrader) | Fulvestrant | Binds & degrades ER | Postmenopausal; metastatic HR+ disease, often after AI failure | Injection site pain, hot flashes, GI upset | IM injection (gluteal); loading dose schedule; caution with bleeding disorders |
| Ovarian Function Suppression (OFS) |
GnRH agonists: Leuprolide, Goserelin, Triptorelin |
Suppress ovarian estrogen production (medical, surgical, or radiation) | Premenopausal HR+; adjuvant or metastatic; used with AI or tamoxifen | Menopausal symptoms, bone loss (GnRH); permanent menopause (surgery/radiation) | Use with AI in premenopausal women for maximal estrogen suppression; surgical/radiation options are irreversible |
Treatment Duration in Early Breast Cancer
- Premenopausal: Tamoxifen ± OFS for 5 years; may extend to 10 years based on risk
- Postmenopausal: AI for 5 years, or AI for 2–3 years followed by tamoxifen to complete 5 years; extended therapy up to 10 years for high-risk
- Switching strategies: Tamoxifen → AI or AI → Tamoxifen depending on tolerance, menopausal status
Pharmacist Monitoring & Counseling
- VTE risk: Tamoxifen — counsel on leg swelling, SOB, chest pain
- Bone health: AIs & OFS — baseline and periodic DEXA scans; recommend calcium + vitamin D, weight-bearing exercise
- Hot flashes: Avoid CYP2D6 inhibitors if on tamoxifen; use venlafaxine or gabapentin if needed
- Adherence: Stress long-term adherence for recurrence risk reduction
- Drug interactions: Especially with tamoxifen (CYP2D6), exemestane (CYP3A4)
Synonyms
Endocrine Therapy