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By Mayo Clinic staffThe 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)