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Causes

By Mayo Clinic staff

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Illustration showing the main parts of the breast Breast anatomy

The exact cause of fibrocystic breast changes isn't known, but experts suspect that reproductive hormones — especially estrogen — play a role.

When examined under a microscope, fibrocystic breast tissue includes distinct components such as:

  • Fluid-filled round or oval sacs (cysts)
  • A prominence of scar-like fibrous tissue (fibrosis)
  • Overgrowth of cells (hyperplasia) lining the milk ducts or milk-producing tissues (lobules) of the breast
  • Enlarged breast lobules (adenosis)

DS01070

Aug. 20, 2008

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