What exactly is intraductal papilloma?

Benign: It is a benign tumor in the milk ducts (of the breast).

Mass in breast: Intraductal papilloma (ip) is the most common cause of bloody nipple discharge. It is a small mass within the duct of the breast. They are usually noncancerous but can sometimes have abnormal cells or an early breast cancer. Once diagnosed on needle biopsy, they are usually completely removed with surgery.