The cancer usually affects the ducts of the nipple first small milk-carrying tubes , then spreads to the nipple surface and the areola the dark circle of skin around the nipple. The nipple and areola often become scaly, red, itchy, and irritated. The unusual changes in the nipple and areola are often the first indication that breast cancer is present. Doctors are not yet completely sure how Paget's disease develops. One possibility is that the cancer cells start growing inside the milk ducts within the breast and then make their way out to the nipple surface.