This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. Breast cancer is one of the most common cancers among women in the United States. Mammograms (breast x-rays) can often find breast cancers at a time when they can be cured. Women whose mammograms show extensive dense (white) areas are more likely to develop breast cancer and are also more likely to have cancers that are missed by mammograms. Women who are childless;use menopausal hormones or have a mother or sister with dense breasts are themselves likely to have dense breasts. In contrast, women who are older;no longer have periods, or are heavy tend to have less dense breasts. It is unclear why some factors lead to having dense breasts and why having dense breasts increases a woman's chances of developing breast cancer. The purpose of this research is to determine why some women's breasts look dense (very white) on mammograms, what types of cells and tissues make up dense areas of breasts, and why such tissues are more likely to become cancer. Few research studies have tried to compare mammograms and matched breast tissues. The researchers conducting this study have developed a plan to address this question. However, before conducting a large study, researchers often conduct a smaller "pilot study" to make sure that the research plan will work well. That is why we are asking you to participate in this pilot study of 250 women. This protocol describes a pilot study to demonstrate the feasibility of a protocol for conducting a full-scale study to elucidate the biologic mechanisms that mediate the substantial breast cancer risk associated with high mammographic density. Specifically, we will develop, fine tune, and validate a complex cross-sectional study protocol to collect risk factor data and biological specimens (blood, buccal cells, tissue fluids, and tissue) required to discover mechanisms and biomarkers that link high mammographic density (as measured quantitatively using computerized methods) to breast cancer risk. We will also develop the methodology for establishing a cohort of women who have undergone a benign biopsy, which will provide a high-risk population in which to prospectively validate markers identified in the cross-sectional component of the study. Women who are recommended for an image-guided breast biopsy following a mammogram will be invited into the study. The radiologist recommending the biopsy will mention the study and give the woman a pamphlet explaining the study. The study coordinator will call the woman and explain the study to her and with verbal consent conduct a 20 minute survey. Consenting women will arrive the day of the biopsy [unreadable] hour early to read and sign the consent form, have blood drawn and a mouthwash sample collected and her height and weight measured. If the participant is still menstruating she will be asked to return a pre-addressed postcard with the date of her first day of her next menstrual period. The participant will be contacted annually for the next 10 years to get current address and any change in health status.