What is the typical duration of treatment with anastrozole (aromatase inhibitor)?

Duration of Anastrozole Treatment

For postmenopausal women with hormone receptor-positive breast cancer, anastrozole should be taken for 5 years as standard initial therapy, with extension to 10 years total for node-positive disease and consideration of extension for higher-risk node-negative disease. 1

Standard Treatment Duration

• The FDA-approved and standard duration is 5 years for adjuvant treatment of early breast cancer in postmenopausal women 2
• In the landmark ATAC trial, anastrozole was administered for five years, establishing this as the evidence-based standard duration 2
• For breast cancer risk reduction in high-risk postmenopausal women, anastrozole 1 mg daily for 5 years significantly reduced breast cancer incidence compared to placebo 3

Extended Therapy: Who Benefits

Node-positive patients derive the most substantial benefit from extended therapy and should be offered treatment up to 10 years total 1, 4

Candidates for Extended Therapy (Beyond 5 Years):

• Node-positive disease: These patients should routinely be offered extended therapy up to 10 years total, as they show the greatest absolute benefit 1
• Higher-risk node-negative disease: Consider extension based on established prognostic factors including young age and high-grade tumors 1, 4
• A recent Japanese trial (AERAS, 2023) demonstrated that continuing anastrozole for an additional 5 years (10 years total) improved 5-year disease-free survival from 86% to 91% (HR 0.61, P<0.001) 5

Patients Who Should NOT Receive Extended Therapy:

• Low-risk node-negative tumors should not routinely receive extended therapy, as the absolute benefits are narrow and may not justify ongoing toxicity 1, 4

Maximum Duration

Women should receive no more than 10 years of total endocrine treatment 1, 4

• There is no evidence supporting benefit beyond 10 years, and toxicity accumulates over time 1, 4
• Do not automatically extend therapy in all patients—carefully assess individual recurrence risk 1

Benefits of Extended Therapy

Extended anastrozole therapy provides:

• Reduced distant recurrence risk: 34% relative risk reduction in disease recurrence 4
• Prevention of contralateral breast cancer: This is a major benefit, with 58% relative risk reduction in new opposite-breast cancers 4
• Reduced local recurrence: The AERAS trial showed fewer local recurrences with extended therapy (10 vs 27 events) 5
• No overall survival benefit: Extended therapy does not improve overall survival, only prevents recurrence and second cancers 1, 4

Toxicity Considerations

The decision to extend therapy must weigh these significant adverse effects:

• Bone-related events: Increased fractures (14% vs 9%), new osteoporosis (11% vs 6%), and bone pain 4
• Cardiovascular events: Trend toward increased risk (OR 1.18) 1, 4
• Musculoskeletal symptoms: Joint stiffness, arthralgia (53-69% of patients), myalgia (28-37%) 3, 6
• Quality of life: Worsening in physical role functioning compared to placebo 1, 4
• Other symptoms: Hot flashes (38-54%), vasomotor symptoms, hypertension, dry eyes, vaginal dryness 3, 6

Bone Health Management

• Women with severe osteoporosis (T score <-4 or >2 vertebral fractures) were excluded from major trials and should consider alternative therapies like tamoxifen or raloxifene 3
• Patients receiving anastrozole should be encouraged to exercise regularly and take adequate calcium and vitamin D supplements 3
• Proactive bone health monitoring is essential, as fracture risk is real and increases with extended therapy 1

Special Populations

Risk Reduction Setting:

• For postmenopausal women at high risk without breast cancer, anastrozole 1 mg daily for 5 years reduces invasive and noninvasive breast cancer incidence 3
• Five-year adherence in prevention trials was 68%, lower than placebo (72%) 3

After DCIS Treatment:

• For postmenopausal women with ER-positive DCIS, anastrozole provides comparable benefit to tamoxifen with different toxicity profile 3
• The NSABP B-35 study showed anastrozole improved 10-year breast cancer-free interval to 93.1% versus 89.1% with tamoxifen 3

Critical Pitfalls to Avoid

• Do not extend beyond 10 years total—no evidence supports this and toxicity accumulates 1, 4
• Do not ignore bone health—the increased fracture risk requires proactive calcium, vitamin D, and monitoring 3, 1
• Do not automatically extend in all node-negative patients—carefully assess recurrence risk using established prognostic factors 1
• Do not dismiss patient-reported symptoms—gynecologic symptoms at 6 months predict lower adherence (HR 0.69) 3