Breast Susceptibility to Carcinogenesis
Published 1996 · J. Russo, I. Russo, G. Calaf
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Abstract
The understanding of the human breast has been a major biological puzzle, mainly due to the fact that the mammary gland seems to be the only organ that is not fully developed at birth (1, 2). No other organ presents such dramatic changes in size, shape and function as does the breast during growth, puberty, pregnancy and lactation (2–4). It is agreed that the developmental phase of the human breast starts as early as the stage of nipple epithelium during embryonic development, continuing steadily with body growth, and undergoing a spurt of growth with lobule formation at puberty. Four different lobular structures have been characterized in the breast of postpubertal women, each one representing sequential developmental stages (3). Lobules type 1 are the most undifferentiated ones. They are also called virginal lobules because they are present in the immature female breast before menarche; and they are composed of clusters of 6 to 11 ductules per lobule. Lobules type 2 evolve from the previous ones and have a more complex morphology, being composed of a higher number of ductular structures per lobule. They progress to lobules type 3 which are characterized by having an average of 80 ductules or alveoli per lobule. They are frequently seen in the breast of women under hormonal stimulation or during pregnancy. Lobules type 4 have been described to be present during the lactational period of the mammary gland, but they are not found in the breast of nulliparous post-pubertal women. Lobules type 4 are considered to be the maximal expression of development and differentiation (3).