Anastrozole vs Tamoxifen in Postmenopausal Women with Hormone Receptor-Positive Breast Cancer

Efficacy Outcomes

The American College of Cardiology and other guideline societies recommend anastrozole as adjuvant therapy for postmenopausal women with hormone receptor-positive breast cancer, demonstrating significantly better disease-free survival, time to recurrence, and a more favorable safety profile, particularly regarding endometrial cancer and thromboembolic events 1
Anastrozole reduces disease recurrence by 17% compared to tamoxifen in hormone receptor-positive patients at 68 months median follow-up, with a hazard ratio of 0.83 and 95% CI 0.73-0.94, P=0.005 2, 3
Time to recurrence is reduced by 26% with anastrozole, with a hazard ratio of 0.74 and 95% CI 0.64-0.87, P=0.0002 2, 4
The NSABP B-35 trial demonstrated a 93.1% 10-year breast cancer-free interval with anastrozole versus 89.1% with tamoxifen, with benefits most apparent after 5 years of follow-up, and a hazard ratio of 0.73 and 95% CI 0.56-0.96, P=0.0234 1

Anastrozole has a significantly lower endometrial cancer risk, with 0.2% vs 0.8% incidence, P=0.02 2, 3, 5
Anastrozole reduces thromboembolic events, with 2.8% vs 4.5% incidence, P=0.0004 2, 3
Anastrozole has fewer cerebrovascular events, with 2.0% vs 2.8% incidence, P=0.03 2, 3
Anastrozole has less vaginal bleeding, with 5.4% vs 10.2% incidence, P<0.0001, and less vaginal discharge, with 3.5% vs 13.2% incidence, P<0.0001 2, 3, 5
Anastrozole has fewer hot flushes, with 35.7% vs 40.9% incidence, P<0.0001 2, 3
Anastrozole has lower treatment discontinuation due to adverse effects, with 11.1% vs 14.3% incidence, P=0.0002 2

All evidence applies exclusively to postmenopausal women, with aromatase inhibitors not adequately suppressing ovarian estrogen synthesis in premenopausal women, making these results inapplicable to that population 2
Anastrozole provides particular benefit in younger postmenopausal patients, under 60 years, with improved breast cancer-free interval 1

For postmenopausal women with hormone receptor-positive early breast cancer, anastrozole 1 mg daily for 5 years is the first-line choice, with superior disease-free survival and recurrence rates, and better tolerated overall with fewer life-threatening complications 1, 7

Never combine anastrozole with tamoxifen, as the combination is no better than tamoxifen alone and reduces anastrozole plasma concentrations by 27% 2, 7
Benefits are most pronounced in hormone receptor-positive disease, with patients with ER-negative disease rarely responding to anastrozole 2, 3