While breasts can come in all shapes and sizes, the breast is usually pear shaped. The breast tissue extends from the second rib to the fold under the breast to the outside of the armpit and rests against the chest muscles. About one third of breast tissue is made up of fat. Each breast has a nipple with milk duct openings. Around each nipple is a darker area - this is called the areola.
The breast tissue is made up of lobes and lobules that produce the milk. The milk flows through ducts that spread like a vine inside the breast connecting the lobes with the duct openings in the nipple. Ducts are common sites for breast cancer. Only about 10% of breast cancers occur in the lobes.