Breast fibroadenoma. Light micrograph of a section through a fibroadenoma in breast tissue. Fibroadenomas, also called cystic mammary dysplasia and fibrocystic disease, are the most common type of benign (non-cancerous) tumour of the breast. They occur most frequently in woman of childbearing age, forming a lump 1-5 centimetres in diameter. They can take a number of different forms and can be removed surgically, rarely becoming cancerous. The type shown here is adenosis and florid duct papillomatosis, where the dilated ducts are filled by papillary ingrowths (frond-like, dark purple) from the wall.