Lumps can occur in different parts of the breast, which include lobules, ducts, nipples and fatty tissue.
Lobules: These are the mammary glands that make breast milk. When cancer occurs in the lobules, it is called lobular cancers.
Ducts: These are small canals that carry the milk from the lobules to the nipples. This is a common place for breast cancer to start, and these cancers are called ductal cancer.
Nipple: It is the opening in the skin, where the small ducts come together to form larger ducts, to secrete the breast milk. Cancer that starts in the nipple, called Paget disease of the breast, is a less common type.
Fatty tissue: The ducts and lobules are surrounded by fat and connective tissue, which help to keep them in place. Although less common, breast cancer can develop in these tissues, and are called phyllodes tumor.
Some breast lumps can also develop in the lining of the blood vessels, which are called angiosarcoma.
About 50% of the breast lumps, originating from the mammary glands or ducts, occur in the upper, outer quadrant of the breast, extending into the armpit; the tissue in these parts is thicker than other parts. About 18% of the breast cancers appear in the nipple region, 11% in lower, outer quadrant, and nearly 6% in the lower, inner quadrant.