RT Book, Section A1 Umbricht, Christopher B. A2 Kuerer, Henry M. SR Print(0) ID 6405207 T1 Chapter 2. Invasion T2 Kuerer's Breast Surgical Oncology YR 2010 FD 2010 PB The McGraw-Hill Companies PP New York, NY SN 978-0-07-160178-8 LK accesssurgery.mhmedical.com/content.aspx?aid=6405207 RD 2024/04/20 AB The anatomic structures in which breast cancer invasion occurs arise as paired mammary glands developing from epithelial thickenings on the ventral surface of the 5-week fetus. A mesenchymal condensation occurs around burgeoning epithelial stalks around the 15th week. A physiologic "invasion" of this mesenchyme by cords of epithelial cells creates columns, which later give rise to the lobular organization of the mammary gland. With the onset of cyclical hormonal secretion at puberty, the hormonally responsive periductal stroma differentiates, and the epithelial columns develop into elongated lactiferous ducts terminating into terminal ducts that give rise to lobuloalveolar structures responsible for breast milk production. The adult breast consists of about 15 to 25 lobes, each associated with a major lactiferous duct terminating in the nipple. The glandular and ductal structures are embedded in specialized, hormone-responsive stromal tissue, which consists of adipose tissue admixed with collagenous and vascular elements, the relative abundance of which is largely responsible for the physical and radiographic appearance of the breast (Fig. 2-1).