Blood samples are obtained for pharmacogenetic studies at baseline, at 6-12 weeks, and then at 1 year. Samples are analyzed for plasma anastrozole concentrations via high-performance liquid chromatography; genotyping for htSNPs via PCR; plasma levels of estradiol, estrone, estrone sulfate, testosterone, and androstenedione via gas chromatographic negative chemical ionization tandem mass spectrometry and liquid chromatographic electrospray tandem mass spectrometry.