Breast nonmalignant

Topic Completed: 1 April 2014

Minor changes: 8 August 2019

Copyright: 2002-2019,, Inc.

PubMed Search: Embryology [title] breast

Belinda Lategan, M.D.
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Cite this page: Lategan B. Embryology. website. Accessed May 30th, 2020.
  • Breast is considered an epidermal gland because it develops as diverticula of epidermis into dermis
  • Also considered a modified and highly specialized apocrine gland
  • Mammary gland development begins at week 4, when ectoderm and underlying mesoderm proliferate and differentiate into skin

  • Week 4: paired ectodermal thickenings called mammary ridges or milk lines develop along ventral embryo and extend in curvilinear convex pattern from axilla to medial thigh; ridges will eventually disappear except at 4th intercostal space on anterior thorax, where mammary gland develops
  • Week 5: remnant of mammary ridge ectoderm proliferates and is termed primary mammary bud
  • Week 7: primary mammary bud grows downward into underlying dermis
  • Week 10: primary mammary bud branches into secondary buds
  • Week 12: secondary mammary buds start lobule development
  • Week 20: small lumina develop within mammary buds that coalesce and elongate to form lactiferous ducts
  • Week 20 - 32: differentiation of mesenchyme into fat
    • Stroma originating from reticular dermis form suspensory ligaments of Cooper attaching breast to skin and subdividing breast into lobes
  • Month 5: areola is formed by ectoderm
  • Week 23 - 28: myoepithelial cells arise from basal cells, playing an important role in branching morphogenesis of the mammary gland via synthesis of basement membrane constituents, growth factors and metalloproteinases
  • Near term birth: nipple formed by evagination of mammary pit
  • References: eMedicine: Breast Embryology, UC Davis: Early Development of the Human Breast, J Mammary Gland Biol Neoplasia 2000;5:119
Diagrams / tables

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Milk lines

Lifetime mammary gland development

Microscopic (histologic) images

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Early branching of the major lactiferous ducts

Doughnut shaped disk

Enlarging breast

Cellular lobules

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