What exactly is atypical intraductal hyperplasia?

Precancerous changes. In breast tissue cells from needle or open surgical biopsy. Your doctor can discuss the significance of this in light of the remainder of your family history, breast examination, mammography, and your overall health. This is not cancer, but may be a sign to be watchful and have regular physician follow-up or further evaluation regarding risk of developing breast cancer.
Abnormal Duct Cells. Atypical duct hyperplasia (ADH (vasopressin)) is an abnormality of the milk ducts which can only be diagnosed by breast biopsy. This is not a pre-cancerous condition, however women with ADH (vasopressin) are known to have a 2-4 fold increase in breast cancer risk. Therefore, women with ADH (vasopressin) should be carefully followed and/or given the option of tamoxifen to reduce the cancer risk.