The Breast

Breast cancer is the most common form of cancer in women. In order to fully understand the molecular causes of breast cancer, it is critical to understand the underlying mechanisms which regulate and dictate normal breast development. Both pituitary and ovarian steroid hormones are required to regulate and govern breast development. Progesterone is an ovarian steroid hormone and is considered to be a major risk factor for the development of breast cancer, since it controls proliferation of stem and progenitor cells. The human breast is organized as an epithelial network of ducts opening at the nipple and these form a tree-like structure ending in lobuloalveolar glands located within the collagenous and adipose tissue of the mammary gland. Upon pregnancy, specialized luminal cells develop in the alveoli which go on to secrete milk proteins and lipids during lactation. Breast development occurs in three well-defined stages: embryonic, pubertal, and reproductive.