It is necessary to give a brief overview of the structure of the breast in order to put into context the various conditions that will be described in this chapter and others. The breast is comprised of fat, connective tissue, and glands (ducts and lobules) (see Fig. 2.1a). The amount of connective tissue also called stroma varies among women. When it is increased it leads to a denser breast, it may make the detection of cancer by mammography more difficult. The ratio of fatty tissue to glandular tissue varies among women and at different times in woman’s life. In younger woman the ratio usually favors the glandular tissue. After menopause as the number of glands diminishes, the ratio favors the fatty. Weight gain or loss affects this ratio as well. The majority of a woman’s glandular tissue is situated near the axilla or under arm, in the upper outer quadrant (about 10 o’clock if you were to imagine the breast with a clock superimposed) where a majority of cancers occur.