Atypical ductal hyperplasia (ADH) is an abnormal production of cells within the duct system of the breast. Women who have atypical ductal hyperplasia have an increased risk of breast cancer.

Atypical ductal hyperplasia is usually discovered by mammography and diagnosed with a biopsy of the breast. Women who have ADH are usually followed closely by a doctor and have a breast exam every 6 months and a mammogram once a year.