Introduction: Aromatase inhibitors (AIs) (anastrozole, letrozole, and exemestane) are the treatment of choice in patients with advanced-stage breast cancer and positive hormone receptors. They have shown superiority over tamoxifen as the first-line therapy in terms of response, particularly in time to progression. Presumably, anastrozole and letrozole are slightly superior to tamoxifen as the first-line therapy for postmenopausal patients with metastatic breast cancer. Materials and Methods: A review of the literature was undertaken using the words AIs, metastatic breast cancer as MeSH descriptors in browsers with evidence of clinical practice guidelines. Systematic revisions and randomized clinical trials retrieved from PubMed, Cochrane, ESMO Clinical Practice Guideline, NICE Guidelines, and Trip database were analyzed. A total of 11 articles met the inclusion criteria. Results: Exemestane was correlated to response
rates (36.2%, 95% confidence interval [CI], 18.5-45.9%) and complete response (6.4%). Anastrozole had a response rate of 46%, 95% CI, 32.2-59.8% and a complete response of 14%. The clinical benefit was 59.6% and 68% in exemestane and anastrozole, respectively. The median disease-free interval (DFI) was 6.1 months (95% CI, 2.5-9.6 months) for patients who received exemestane and 12.1 months (95% CI, 7.3-16.8 months) for the patients receiving anastrozole. Discussion: Endocrine therapy is a feasible method to palliate patients with metastatic breast cancer. AIs are the election treatment in postmenopausal patients because of the improvement they achieve in DFI. Conclusion: As a rule, letrozole and exemestane are the best drugs due to their response rates (without significant differences in overall survival or DFI), compared with anastrozole.