Mills Ch3 Breast

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SECTION II : Breast

A

B

FIGURE 3.18  Postmenopausal breast tissue. A: This sample consists primarily of fatty stroma with a few atro- phic ductules. B: In this specimen, a few residual, atrophic lobular acini are evident in a fibrotic stroma, which has replaced the normal, loose intralobular stroma.

intercostal veins, which drain posteriorly into the vertebral veins and the vertebral plexus (8,68).

THE ADULT MALE BREAST The adult male breast, like the female breast, is composed of glandular epithelial elements embedded in a stroma that is composed of varying amounts of collagen and adipose tis- sue. However, in contrast to the adult female breast, the epithelial elements of the male breast normally consist of branching ducts without lobule formation.

LYMPHATIC DRAINAGE Lymphatic drainage of the breast occurs through four routes: cutaneous, axillary, internal thoracic, and pos- terior intercostal lymphatics. The cutaneous lymphatic drainage system consists of both a superficial plexus of channels that lie within the dermis overlying the breast and a deeper network of lymphatic channels that runs with the mammary ducts in the subareolar area. Most of these cutaneous channels drain to the ipsilateral axilla. Cutaneous lymphatics from the inferior aspect of the breast may drain to the epigastric plexus and ultimately to the lymphatic channels of the liver and intra-abdominal lymph nodes. There are three lymphatic drainage pathways in the mammary parenchyma. The most important drainage basin for lymphatic flow from the breast is the axilla, and the axillary lymph nodes receive the vast majority of the lymph drained. The internal thoracic lymphatic route car- ries less than 10% of the lymphatic flow from the breast and ultimately terminates in the internal mammary lymph nodes (7). Drainage eventually empties into the great veins via the thoracic duct, the lower cervical nodes, or the jugular–subclavian confluence. The third and least impor- tant route of mammary lymphatic drainage is the poste- rior intercostal lymphatics, which drain into the posterior intercostal lymph nodes. An understanding of the lym- phatic drainage of the breast is of particular importance in the current era of sentinel lymph node biopsy since this explains the occasional finding of sentinel lymph nodes outside of the axilla (5,7,8).

BIOLOGIC MARKERS, IMMUNOPHENOTYPE, AND MOLECULAR BIOLOGY

Estrogen Receptor and Progesterone Receptor It is now known that there are at least two different ERs, ER α and ER β ; ER α has been far more extensively studied. Using immunohistochemistry, ER α expression can be dem- onstrated in the nuclei of both ductal and lobular epithe- lial cells, with a higher proportion in lobules than in ducts. However, even in the lobules, only a small proportion of the cells show ER α immunoreactivity. Most often, ER α - positive cells in the lobules are distributed singly, admixed with and surrounded by ER α -negative cells (Fig. 3.19) (69). Furthermore, there is considerable heterogeneity in stain- ing for ER α among lobules in the same breast. Of interest, in breast tissue from premenopausal women, there is gen- erally an inverse relationship between expression of ER α and markers of cell proliferation. In particular, most ER α - positive cells do not show expression of the proliferation- related antigen Ki-67, and Ki-67–positive cells are typically ER α -negative. The proportion of ER α -positive cells gradu- ally increases with age but remains relatively stable after the menopause. The incidence of lobules showing contiguous