Effect of anastrozole and tamoxifen as adjuvant treatment for early-stage breast cancer: 100-month analysis of the...

Area of Science:

• Oncology
• Pharmacology

Background:

• Limited data exist on long-term efficacy and side-effect persistence of aromatase inhibitors beyond 5 years.
• The Arimidex, Tamoxifen, Alone or in Combination (ATAC) trial provides a unique opportunity to assess long-term outcomes.

Purpose of the Study:

• To evaluate long-term outcomes, including efficacy and safety, of anastrozole compared to tamoxifen in adjuvant breast cancer treatment.
• To determine if efficacy benefits and side-effects persist after 5 years of treatment.

Main Methods:

• Analysis of postmenopausal women with localized invasive breast cancer from the ATAC trial.
• Primary endpoint: disease-free survival (DFS). Secondary endpoints: time to recurrence (TTR), contralateral breast cancer (CLBC), time to distant recurrence (TTDR), overall survival (OS), and deaths after recurrence.
• Safety data, including fractures and adverse events, were collected blindly throughout the study.

Main Results:

• Anastrozole demonstrated significantly improved DFS, TTR, TTDR, and CLBC in both intention-to-treat (ITT) and hormone-receptor-positive populations at a median follow-up of 100 months.
• Recurrence rates remained significantly lower on anastrozole compared to tamoxifen even after treatment completion, indicating a carryover effect.
• Fracture rates were higher with anastrozole during treatment but comparable after cessation. No significant differences in cardiovascular events were observed.

Conclusions:

• Anastrozole offers clear long-term efficacy advantages over tamoxifen as initial adjuvant therapy for hormone-sensitive early breast cancer.
• Statistically significant evidence supports a larger carryover effect of anastrozole compared to tamoxifen after 5 years of adjuvant treatment.
• Long-term safety findings suggest a manageable side-effect profile for anastrozole in this patient population.