ABSTRACT

As a prelude to discussing mechanisms of carcinogenesis, it is important to understand breast development and differentiation. The anatomical features of the mammary gland are illustrated in Figure 16.1. The human mammary gland is comprised of 12 to 20 segments defined as the branching ductular and lobular components emanating from a single lactiferous collecting duct. The human mammary gland undergoes unique phases of growth and differentiation in a particular age and in hormonally regulated fashion. At birth the breast is a palpable structure in both sexes, comprised of a nipple and collecting ducts. In addition there is a large interindividual variation that ranges from no additional branching to a well-developed dichotomous branching system with the formation of rudimentary lobules [1]. During the first two years of life in both sexes, the mammary gland undergoes a functional differentiation including production and secretion of casein, cystic dilatation with apocrine metaplasia, and involution with accumulation of a dense matrix surrounding atrophic ducts or lobules [1]. There is no apparent correlation between structural morphology and epithelial differentiation at this stage.