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By Mayo Clinic staffEach of your breasts contains 15 to 20 lobes of glandular tissue, arranged like the petals of a daisy. The lobes are further divided into smaller lobules that produce milk during pregnancy and breast-feeding. Small ducts conduct the milk to a reservoir that lies just beneath your nipple. Supporting this network is a deeper layer of connective tissue called stroma. Fibroadenomas are made up of both glandular (lobular) tissue and connective (stromal) tissue.
The cause of fibroadenomas is unknown. However, fibroadenoma development is probably related to reproductive hormones. Fibroadenomas occur in greater frequency during your reproductive years, can increase in size during pregnancy or with estrogen therapy, and tend to shrink after menopause.
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