With the development of highly effective, well-tolerated third-generation 
aromatase inhibitors (AIs), these drugs will probably play an increasingly 
important role in all phases of breast cancer treatment. As a result, the impact 
of such hormonal agents on patients' quality of life bears rigorous 
investigation. In a randomized, multicenter, single-blind cross-over study, the 
AIs letrozole and anastrozole were evaluated for quality of life, toxicity, and 
patient preference. A total of 72 patients were enrolled and were treated with 
each drug for a 4-week period, with a 1-week drug-free washout period before 
cross-over to the alternate agent. Assessments included the FACT-ES, toxicity, 
and patient preference. The FACT-ES is a validated questionnaire designed to 
measure quality of life of women with breast cancer who are being treated with 
endocrine therapies. Letrozole was superior to anastrozole with respect to both 
quality of life and toxicity evaluations. In addition, at the conclusion of the 
trial, reduced nausea, hot flashes, and abdominal discomfort caused almost twice 
as many patients to prefer to continue with letrozole therapy than with 
anastrozole. Data from this recent trial indicate that letrozole is better 
tolerated and provides better quality of life than anastrozole for women with 
metastatic breast cancer.