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 (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.

Inclusion Criteria:

- Patients receiving tamoxifen for adjuvant therapy of breast cancer or ductal carcinoma
in situ, or as chemoprevention

- Age 18 years and above

- May be pre- and post-menopausal

- Females

- Patients may be at any point in their hormonal treatment, but must have completed any
planned surgery, radiation and chemotherapy

- Must use a reliable form of birth control

Exclusion Criteria:

- Pregnant

- Breastfeeding

- Concurrent use of corticosteroids, megestrol, or phenobarbital

- History of allergy to tamoxifen

- Unwilling to have a yearly gynecological exam