The patients for this study will have early stage breast cancer that is potentially curable. This type of cancer usually treated with certain hormonal therapy such as Tamoxifen pills in order to reduce the chance of cancer recurrence. Tamoxifen has been shown to reduce the risk of recurrence of hormonal receptor positive breast cancer (also referred to estrogen receptor and progesterone receptor positive breast cancer). However Tamoxifen does not work equally well to everyone and certain patients may develop recurrence despite appropriate therapy. The reasons for failure of tamoxifen in these patients are not fully elucidate and is a subject of intense research. This study will help us better understand the interaction between the hormonal therapy Tamoxifen, estrogen receptors and certain genes in the cancer cell. This knowledge may eventually help us to choose appropriate therapy in the future patients with the same type of cancer.