Class & Mechanism:
- Selective Estrogen Receptor Modulator (SERM)
- Antagonist on estrogen receptors in breast and uterine tissue, agonist on estrogen receptors in bone and lipid metabolism.
- Unlike tamoxifen, no agonist activity in the endometrium, so no increased endometrial cancer risk.
Oncology & Preventive Indications:
- Primary prevention of invasive breast cancer in postmenopausal women at high risk (e.g., LCIS, strong family history, Gail model ≥1.66%).
- Not used for treatment of established breast cancer.
- Also indicated for prevention and treatment of postmenopausal osteoporosis (dual benefit in some patients).
Dose & Administration:
- 60 mg orally once daily, with or without food.
Pharmacist Considerations:
Advantages in Oncology Prevention Setting:
- Reduces risk of ER+ invasive breast cancer by ~50% in high-risk postmenopausal women.
- Lower incidence of endometrial cancer vs tamoxifen.
Adverse Effects:
- Common: hot flashes, leg cramps, peripheral edema.
- Serious: increased risk of venous thromboembolism (DVT, PE) — similar magnitude to tamoxifen.
- No increased risk of endometrial carcinoma.
Monitoring:
- Monitor for VTE symptoms (leg swelling, pain, sudden shortness of breath).
- Bone mineral density (if also used for osteoporosis).
Counseling Points:
- Advise patients to remain active and avoid prolonged immobility to reduce VTE risk.
- Report any unexplained vaginal bleeding (rare, but warrants evaluation).
- Not recommended for premenopausal women or for treatment of existing breast cancer.
Drug Interactions:
- Minimal CYP metabolism — fewer drug-drug interactions compared to tamoxifen.
- Use caution with other drugs that increase clotting risk.