Anastrozole Treatment for Postmenopausal Women with Breast Cancer
For postmenopausal women with hormone receptor-positive breast cancer, anastrozole 1 mg orally once daily is the recommended dose, administered for 5 years in the adjuvant setting. 1
Standard Dosing Regimen
- The FDA-approved dose is 1 mg taken once daily, which can be taken with or without food. 1
- For adjuvant treatment of early breast cancer, the optimal duration is 5 years based on the ATAC trial data. 1
- For advanced breast cancer, anastrozole should be continued until tumor progression occurs. 1
Clinical Indications
Adjuvant Treatment
- Anastrozole 1 mg/day is one of three recommended aromatase inhibitors (along with letrozole and exemestane) for postmenopausal women with hormone receptor-positive breast cancer. 2
Risk Reduction
- For breast cancer risk reduction in high-risk postmenopausal women, anastrozole 1 mg/day for 5 years is now an ASCO-endorsed option alongside exemestane, raloxifene, or tamoxifen. 3
- Women most likely to benefit include those with atypical hyperplasia, lobular carcinoma in situ, 5-year BCRAT risk ≥3%, or 10-year IBIS/Tyrer-Cuzick risk ≥5%. 3
- Long-term follow-up from IBIS-II demonstrates a 49% reduction in breast cancer incidence (HR 0.51, p<0.0001) with continued benefit extending beyond the 5-year treatment period. 4
Critical Contraindications
- Anastrozole must never be prescribed to premenopausal women for any indication—this is an absolute contraindication. 3, 5
- Severe osteoporosis (T-score <-4 or more than two vertebral fractures) is a contraindication due to accelerated bone loss risk. 5
Mandatory Pre-Treatment Assessment
Before initiating anastrozole, clinicians must:
- Evaluate baseline fracture risk and measure bone mineral density (BMD) via DEXA scan. 2, 5
- Use caution in patients with moderate bone mineral density loss and consider bone-protective agents. 2
Essential Monitoring and Bone Protection
Bone Health Management
- All patients must receive calcium and vitamin D supplementation throughout treatment. 2, 5
- Regular weight-bearing exercise should be prescribed to maintain bone density. 2, 5
- For patients with moderate bone loss, consider bisphosphonates or RANKL inhibitors prophylactically. 2, 5
- Serial BMD monitoring is required during treatment to detect accelerated bone loss. 5
Common Side Effects to Counsel Patients About
- Joint stiffness and arthralgias are very common and should be anticipated. 2, 5
- Vasomotor symptoms (hot flashes) occur frequently. 2, 5
- Hypertension, dry eyes, and vaginal dryness are additional common effects. 2
- Gastrointestinal disturbances occur in 29-33% of patients but are generally mild and transient. 6, 7
Special Populations
Renal and Hepatic Impairment
- No dose adjustment is necessary for patients with renal impairment or elderly patients. 1
- No dose changes are recommended for mild-to-moderate hepatic impairment. 1
- Anastrozole has not been studied in severe hepatic impairment and should be avoided. 1
Clinical Efficacy Data
- In advanced breast cancer after tamoxifen failure, anastrozole 1 mg demonstrated superior survival compared to megestrol acetate (median 26.7 vs 22.5 months, HR 0.78, p<0.025). 8
- The 1 mg dose achieves maximal estrogen suppression (58.3% reduction in plasma estradiol) and is more effective than the 10 mg dose. 9, 7
- Response rates in advanced disease range from 21-27% with stable disease ≥24 weeks. 6, 7
Treatment Selection Considerations
The choice between anastrozole and other aromatase inhibitors should account for the patient's baseline comorbidities and adverse effect profiles, particularly bone health status and cardiovascular risk factors. 2