A group of conditions marked by changes in breast tissue that are benign (not cancer). There are different types of mammary dysplasia, including some types caused by an increase in the number of cells or by the growth of abnormal cells in the breast ducts or lobes. Signs and symptoms of mammary dysplasia include irregular lumps or cysts, breast swelling or discomfort, skin redness or thickening, and nipple discharge. Most benign breast conditions do not increase the risk of breast cancer. Also called benign breast disease.