II. Indications
-
Breast Cancer in post-menopausal women (Estrogen Receptor positive)
- Original recommendations were for 5 year course following Breast Cancer Management
- As of 2013, ten year course is recommended following Breast Cancer Diagnosis
- Breast Cancer recurrence prevention (NNT 27) who extend their Tamoxifen course from 5 to 10 years
- Benefits still outweigh risks of Endometrial Cancer and Venous Thromboembolism
- Davies (2013) Lancet 381(9869):805-16 +PMID: 23219286 [PubMed]
- Breast Cancer Prevention in pre-Menopause or post-Menopause
- Breast Cancer risk >1.66% in 5 years and age over 35 years old
- Higher efficacy than Raloxifene for breast Cancer Prevention
- However also higher Venous Thromboembolism and Endometrial Cancer Risks
- Unlike Tamoxifen, Raloxifene is not approved for pre-menopausal breast Cancer Prevention
III. Contraindications
- Venous Thromboembolism history
- Perioperative period
- Prolonged immobilization (discontinue 72 hours before expected immobilization)
- History of Cerebrovascular Accident (CVA) or Transient Ischemic Attack (TIA)
IV. Mechanism
- See Selective Estrogen Receptor Modulator
- Positive Estrogen effects
- Stimulates bone mineralization
- Improves lipid profile
- Anti-Estrogenic effects
- No Breast stimulation
- No uterine stimulation
V. Dosing
-
Breast Cancer
- Tamoxifen 10 to 20 mg orally twice daily for 5 to 10 years
- Breast Cancer Prevention
- Tamoxifen 20 mg daily for 5 years
VI. Adverse Effects
- Precautions
- Thromboembolism, Uterine Cancer and Cardiovascular Risk are FDA black box warnings
-
Thromboembolism
- Tamoxifen significantly increases risk
- Associated with 4 cases per 1000 women on Tamoxifen for 5 years
-
Endometrial Cancer (risks apply to postmenopausal women)
- Markedly increased risk if used more than 5 years
- Associated with 4 cases per 1000 women on Tamoxifen for 5 years
- Relative Risk for 2 to 5 years of use: 2.0
- Relative Risk for 5 or more years of use: 6.9
-
Hot Flashes
- See Hot Flashes for management
- Avoid symptomatic management with agents contraindicated following Breast Cancer
- Avoid Estrogen and Phytoestrogens
- Avoid Paroxetine and Fluoxetine (see below)
- Other adverse effects
- Alopecia
- Cataracts
- Eye Exam every 1-2 years
- Lab abnormalities
- Hypercalcemia
- Liver Function Test abnormalities
VII. Safety
- Avoid in Lactation
- Avoid in pregnancy
- Use reliable Contraception for at least 2 months after completing Tamoxifen
- Monitoring
VIII. Efficacy
-
Estrogen Receptor Positive Breast Cancer
- Reduces Breast Cancer recurrence (29%)
- Reduces mortality from Breast Cancer (20%)
- Anti-Estrogen
- Reduces Breast Cancer recurrence rate
- Preserves Bone Mineral Density
- Only applies to post-menopausal patients
- Bone Mineral Density decreases if premenopausal
- Lowers Total Cholesterol and LDL Cholesterol
- Only applies to post-menopausal patients
- No effect on lipids if premenopausal
- Reference
IX. Drug Interactions
-
CYP2D6 Inhibitors (e.g. Paroxetine, Fluoxetine, Bupropion)
- May decrease Tamoxifen efficacy (avoid these CYP2D6 Inhibitors in Breast Cancer patients)
- Oral Anticoagulants
- Tamoxifen may effect bleeding risk
X. Resources
Images: Related links to external sites (from Bing)
Related Studies
| tamoxifen (on 12/21/2022 at Medicaid.Gov Survey of pharmacy drug pricing) | ||
| TAMOXIFEN 10 MG TABLET | Generic | $0.18 each |
| TAMOXIFEN 20 MG TABLET | Generic | $0.33 each |