Atypical ductal hyperplasia (ADH) is an abnormal overgrowth of cells within the milk ducts of the breast. ADH is not cancer. But having ADH increases the risk of breast cancer.

ADH is usually found with a mammogram. It is diagnosed with a biopsy of the breast. If you have ADH, it is important to have follow-up testing to watch for breast cancer. You may need to have a breast exam every 6 months and a mammogram once a year.