What is Arimidex (anastrozole) used for?

Uses of Arimidex (Anastrozole)

Arimidex (anastrozole) is primarily used as an adjuvant treatment for postmenopausal women with hormone receptor-positive early-stage breast cancer, and for the treatment of advanced breast cancer in postmenopausal women. 1

Primary Indications

Arimidex is FDA-approved for:

• Adjuvant treatment of early breast cancer:

  • First-line treatment in postmenopausal women with hormone receptor-positive early breast cancer 2
  • After 2-3 years of tamoxifen to complete a total of 5 years of endocrine therapy 3
  • Extended therapy for 5 years after completing 5 years of tamoxifen 3

• Treatment of advanced breast cancer:

  • First-line treatment for postmenopausal women with hormone receptor-positive or hormone receptor-unknown locally advanced or metastatic breast cancer 2
  • Second-line treatment for advanced breast cancer in postmenopausal women whose disease has progressed after tamoxifen therapy 1

Mechanism of Action

Anastrozole works by:

• Selectively inhibiting the aromatase enzyme, which converts androgens to estrogens 1
• Reducing serum estradiol concentrations by approximately 70% within 24 hours and by approximately 80% after 14 days 1
• Suppressing intratumoral estrogen levels (E2, E1, and E1S) by 89%, 83.4%, and 72.9% respectively 4

Clinical Benefits

The clinical advantages of Arimidex include:

• Improved disease-free survival compared to tamoxifen (HR 0.87; 95% CI, 0.78-0.97) 3
• Reduced time to recurrence compared to tamoxifen (HR 0.79; 95% CI, 0.70-0.90) 3
• Lower risk of contralateral breast cancer compared to tamoxifen in hormone receptor-positive patients 5
• Fewer thromboembolic events, cerebrovascular events, and endometrial cancer compared to tamoxifen 3

Important Considerations

• Contraindications:

  • Premenopausal women (does not adequately suppress ovarian estrogen synthesis) 3, 2
  • Pregnancy or potential for pregnancy 1
  • History of severe allergic reaction to anastrozole 1

• Side Effects:

  • Increased risk of bone fractures (11% vs 7.7% with tamoxifen) 3
  • Arthralgias and musculoskeletal disorders 3, 2
  • Vasomotor symptoms (hot flashes) 2
  • Hypertension and dry eyes 2

• Monitoring Requirements:

  • Baseline fracture risk assessment and bone mineral density measurement 2
  • Monitoring for musculoskeletal symptoms 2

Special Populations

• Risk Reduction: Anastrozole (1 mg/day) can be used for breast cancer risk reduction in postmenopausal women at increased risk 2

• DCIS: May be considered to reduce the risk of ipsilateral breast cancer recurrence in postmenopausal women with ER-positive DCIS treated with breast-conserving therapy 2

• Switching Strategy: Women who have received 2-3 years of tamoxifen should consider switching to anastrozole to complete a total of 5 years of endocrine therapy 2

The optimal duration of anastrozole therapy in the adjuvant setting is typically 5 years, though ongoing research continues to evaluate extended therapy options 2.