The purpose of this research is to try to identify which women who take tamoxifen are likely to suffer from hot flashes or are more likely to have other side effects or benefits from the drug. The researchers will do so by determining whether there are mutations that normally occur in human DNA that might influence the way individuals respond to medications.

The study will test the following hypotheses.

1. There is a relationship between genetically distinct metabolic profiles of tamoxifen and the frequency and severity of hot flashes in women on chronic tamoxifen therapy.
2. Genetically distinct metabolic profiles for tamoxifen effect lipid profile, bone turnover metabolites and bone mineral density, and coagulation factors.
3. Different genetic profiles of estrogen responsive genes influence the pharmacodynamic effects of tamoxifen in cardiovascular system.

Inclusion Criteria:

1. 18-years or older
2. Women with a prior breast cancer or who are at a high risk for developing the disease and about to start tamoxifen therapy.
3. Participants must not be treated with concomitant chemotherapy or hormone therapy other than tamoxifen. They must not have ovarian ablation or currently being treated with radiation therapy and/or chronic corticosteroids.
4. The participant must not be taking anti-hot flash therapy (clonidine, bellergal, megestrol acetate). Vitamin E, selective serotonin reuptake inhibitors, or herbal remedies are allowed provided that the participant has been taking the remedy for at least 4 weeks and intends to continue the remedy for at least the first month while on the study, and allows for one-month follow up evaluation (hot flash diaries and blood samples).
5. The participant must not be pregnant or lactating.
6. The participant is able and willing to sign an informed consent.

Eligible patients included women 18 years or older, non-pregnant or lactating, who were recommended tamoxifen for adjuvant treatment or for the prevention of breast cancer from the oncology clinics.