scientists do not know exactly what causes paget's disease of the nipple but two major theories have been suggested for how it develops. one theory proposes that cancer cells called paget cells break off from a tumor inside the breast and move through the milk ducts to the surface of the nipple resulting in paget's disease of the nipple. this theory is supported by the fact that more than 97% of patients with paget's disease also have underlying invasive breast cancer or ductal carcinoma in situ (dcis). dcis also called intraductal carcinoma is a condition in which abnormal cells are present only in the lining of the milk ducts in the breast and have not invaded surrounding tissue or spread to the lymph nodes. dcis sometimes becomes invasive breast cancer. invasive breast cancer is cancer that has spread outside the duct into the breast tissue and possibly into the lymph nodes under the arm or into other parts of the body. the other theory suggests that skin cells of the nipple spontaneously become paget cells. this theory is supported by the rare cases of paget's disease in which there is no underlying breast cancer and the cases in which the underlying breast cancer is found to be a separate tumor from the paget's disease.
what are the possible causes of paget's disease of the nipple?