Anatomy of the breast (diagrammatic sagittal section) Anatomy of the breast (diagrammatic sagittal section). The ductal system extends from the nipple to multiple lobes of terminal-duct lobular units (TDLUs) branching in a treelike fashion. The TDLU is the site of origin for most breast carcinomas. The ducts and lobular acini are lined by two layers of cells: the inner luminal cells and outer myoepithelial cells. (Reproduced with permission from McKinley M, O'Loughlin VD. Human Anatomy, 2nd ed. New York: McGraw-Hill; 2008.) Source: Breast Pathology, Pathology: A Modern Case Study Citation: Reisner HM. Pathology: A Modern Case Study; 2015 Available at: https://accessmedicine.mhmedical.com/DownloadImage.aspx?image=/data/Books/1569/rei_ch16_f002.png&sec=95971199&BookID=1569&ChapterSecID=95971193&imagename= Accessed: October 14, 2017 Copyright © 2017 McGraw-Hill Education. All rights reserved