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

If you aren't yet menopausal, your discomfort may result from the way your hormone levels fluctuate during your menstrual cycle. The fluctuations can make your breasts have areas of lumpy thickening that feel tender, sore and swollen. Those fibrocystic breast changes often feel the worst before your menstrual period, and the pain and lumpiness tends to clear up once your menstrual period begins.

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)
Mar. 08, 2013