Chest muscles move your arm through a normal range of motion. Axillary lymph nodes filter lymph fluid from your breast and help your body fight infections. Fatty tissue adds to the size of your breast and provides shape. During normal breast cell growth, the cells reproduce or divide in a controlled way, following a series of well-defined steps. Simply, breast cancer occurs when cells in the breast grow abnormally.
Cancer cells differ from normal cells in several ways.
They vary in size and shape. They divide quickly and sometimes move into other areas of body tissue. Cancer may appear as a lump, with about 50 percent usually found in the upper-outer section of the breast. Most lumps detected in breast tissue are not of concern. A fibrocystic breast change, for example, is a common benign breast condition that you may notice and associate with a change in the texture or firmness of your breast.