Paget's disease of the nipple, although recognized since 1874, remains in several respects enigmatic. The two main theories of its origin are 1) epidermotropic, i.e. ductal cancer cells migrating to the epidermis of the nipple, and 2) in situ appearance of malignant keratinocytes expressing the multicentricity of breast cancer. The literature is reviewed. Clinical, histologic (including classification), histochemical and electron microscopy observations and diagnostic considerations are discussed. Diagnosis is often delayed, with adverse consequences for treatment. The nipple lesions may be accompanied by ductal carcinoma of local or more extensive in situ type, or invasive tumour. Lymph-node metastasis seems to be the most important prognostic factor. The merits of radical vs. modified radical mastectomy and local excision, with or without adjuvant radiotherapy, are considered. Major studies of breast-conserving management of Paget's disease of the nipple are in progress.
