Mills Ch3 Breast

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Breast Laura C. Collins  ■  Stuart J. Schnitt

EMBRYOLOGY  69

THE ADULT MALE BREAST  80

ADOLESCENCE  70

BIOLOGIC MARKERS, IMMUNOPHENOTYPE, AND MOLECULAR BIOLOGY  80

THE ADULT FEMALE BREAST  71

Estrogen Receptor and Progesterone Receptor  80 Other Biomarkers and Immunophenotypic Features  81 Molecular Markers  81 CONCLUSION  81

PREGNANCY AND LACTATION  78

MENOPAUSE  79

BLOOD SUPPLY  79

REFERENCES  81

LYMPHATIC DRAINAGE  80

Advances in breast imaging have provided a variety of noninvasive means to assist in the evaluation of patients with breast disorders (1–4). Nevertheless, at the present time, histologic examination of tissue specimens remains the cornerstone for the diagnosis of breast diseases, and an understanding of normal breast histology is essential for accurate evaluation of such specimens. It should be noted, however, that what constitutes “normal” histology in the breast varies according to gender, age, menopausal status, phase of the menstrual cycle, pregnancy, and lac- tation, among other factors. Therefore, determination of whether a given breast specimen is normal or shows pathologic alterations must take these variables into con- sideration. EMBRYOLOGY Development of the human mammary gland begins during the 5th week of gestation, at which time thickenings of the ectoderm appear on the ventral surface of the fetus. These

mammary ridges, also known as milk lines, extend from the axilla to the groin. Except for a small area in the pectoral region, the bulk of these ridges normally regress as the fetus continues to develop. Failure of regression of other portions of the milk lines can result in the appearance in postnatal life of ectopic mammary tissue or accessory nipples anywhere along the milk lines; this phenomenon is most commonly encoun- tered in the axilla, inframammary fold, and vulva (5–7). The earliest stages of breast development are largely inde- pendent of sex steroid hormones (8). After the 15th week of gestation, the developing breast exhibits transient sensitivity to testosterone, which acts primarily on the mesenchyme. Under the influence of testosterone, the mesenchyme con- denses around an epithelial stalk on the chest wall to form the breast bud, the site of mammary gland development. Solid epithelial columns then develop within the mesen- chyme, and these ultimately give rise to the lobes or seg- ments of the mammary gland. Portions of the fetal papillary dermis encase the developing epithelial cords and eventu- ally give rise to the vascularized fibrous connective tissue that surrounds and invests the mammary ducts and lobules. The more collagen-rich reticular dermis extends into the breast to form the suspensory ligaments of Cooper, which attach the breast parenchyma to the skin. Portions of the mesenchyme differentiate into fat within the collagenous stroma between the 20th and 32nd weeks of gestation.

This chapter is an update of a previous version authored by Laura C. Collins and Stuart J. Schnitt.

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