Breast Stem Cells in Women at Average Risk and Increased Risk for Breast Cancer

Background: * Research suggests that breast cancers may arise from a population of stem cells in the normal mammary gland that produce clones of cancer cells. * Researchers are now trying to determine what events may initiate the formation of cancer cells. Objectives: * To look for and describe breast stem cells from normal breast tissue from women who do not have breast cancer. * To compare the breast stem cells between women at increased risk for breast cancer and women at average risk for breast cancer. * To show a relationship between the number and type of breast stem cells with the density (appearance) of the mammogram (breast x-ray). * To make cell cultures (grow cells under controlled conditions) from the breast stem cells. Eligibility: -Women 18 years of age and older who are at average or increased risk for breast cancer. Design: Participants complete a health history questionnaire, family history questionnaire and risk assessment questionnaire. * Participants have a mammogram and breast biopsy (surgical removal of a sample of breast tissue). * Women who can become pregnant have a urine pregnancy test....