Basic Breast Anatomy

The diagram below (and on Title Page) shows some basic anatomical relationships of the breast. These components are of interest in a discussion about DCIS.

• Normally, each breast has one mammary gland, which attached to the chest wall by ligaments, on either side of the breast bone (sternum).
• The breast rests on the major chest muscle, the pectoralis major. A layer of fat surrounds the glands and extends throughout the breast.
• Each breast, or mammary gland, contains 15-20 lobes, arranged in a circular fashion. Fat covers the lobes and gives the breast it's size and shape.
• Each lobe is comprised of many lobules. Each lobule consists of a cluster of blind-ending ductules, or alveoli. The tiny sac-like alveoli at the end of the lobule is where the milk is produced. A fine net of muscle fibers (myoepithelial cells) surround each alveolus. Visual, auditory and areola stimulation trigger a neuroendocrine reflex which releases oxytocin from the posterior pituitary. Oxytocin travels in the blood to the mammary gland where it stimulates specific receptors on myoepithelial cells, causing them to contract and expel milk into the ducts and on toward the nipple.
• The duct system of each lobe drains into lactiferous sinus.
• Beneath the areola (pigmented skin around the nipple), each duct has a dilated portion called the lactiferous sinus. A suckling baby essentially squeezes the milk out of these sinuses.
• The lobes contain lobules, lobules contain alveoli, alveoli connect to ducts, ducts drain into the lactiferous sinuses, the lactiferous sinuses express milk through the nipple.

DCIS develops in epithelial cells.

• Ductal Carcinoma in Situ is diagnosed when abnormal epithelial cells grow into the lumen of the ducts.
• Rapid cell growth and death leave calcified debris in the lumen. Calcified deposits become visible in mammograms.
• DCIS cells are confined within the ducts from which they arise. The diagnosis changes to invasive breast cancer when abnormal cells erode through the wall of ducts and move into surrounding tissue.