Fibroadenosis or fibrocystic disease is the most common cause of breast lumps in women of reproductive age. The peak incidence is between 35 and 50 years of age. It is rare before 25 years.
The term embraces a spectrum of histologic changes, and may encompass many patients who have cystic lesions detected clinically or sclerotic breast lesions detected on mammography as discussed elsewhere.
Histologically it is characterized by overgrowth of both fibrous stroma, and of epithelial elements i.e. ducts and lobules, in differing proportions. These changes may be considered as abberations of normal breast involution and not part of a disease process. The condition may be due to a disordered or imbalanced response to endogenous sex hormones.
Only in those cases showing marked epithelial hyperplasia - epitheliosis - is the risk of breast carcinoma thought to be increased.