Effect of Pharmacogenomics Differences in Phase I and II Metabolism of Tamoxifen on Efficacy and Toxicity

This study will be an open-label prospective observational trial designed to test associations between polymorphisms of candidate genes and tamoxifen. Pre- and post-menopausal women taking tamoxifen as standard therapy or chemopreventive therapy will be included in this study.

This study will be an open-label prospective observational trial designed to test associations between polymorphisms of candidate genes (focusing initially on the UGT2B7 enzyme) and tamoxifen (TAM) toxicity. Pre- \& post-menopausal women (aged ≥18 years) taking TAM (20 mg/day) as standard therapy or chemopreventive therapy will be included in this study. Patients will be enrolled after they complete all primary surgery, radiation, and adjuvant chemotherapy. Patients will be excluded if they are undergoing other adjuvant endocrine therapies. Other reasons for exclusion will include patients who are pregnant or lactating, or are currently on corticosteroids, phenobarbital, or megestrol acetate. The goal will be to recruit a total of 45 eligible patients over a 1 year accrual period. The investigators expect to treat \~50 new patients per year with TAM at the standard dose of 20 mg/day.