Breast fibroadenoma. Light micrograph of a fibroadenoma, the most common type of benign tumour of the breast. It is also called cystic mammary dysplasia and fibrocystic disease. Here, the connective tissue element of the breast (pink, bottom left and right) has proliferated and become fibrous. Also seen are neoplastic ducts (purple, centre) that are larger than found in normal breast tissue. Fibroadenoma tumours occur most frequently in young woman under 30, and may form a lump 1-5 centimetres in diameter. They can be removed surgically and rarely become cancerous.