Paget's disease of the epidermis typically arises in association with deeply seated mammary or apocrine sweat gland carcinoma; however, it may also be seen when invasive neoplasm involves the skin. A patient treated by simple mastectomy for infiltrating duct carcinoma had a recurrence in the operative area 11 years later which also metastasized to the ipsilateral arm, involved the overlying epidermis, and resulted in pagetoid changes. Noteworthy features are that the Paget lesion may occur in the skin overlying either primary or metastatic mammary carcinoma, the "Paget cells" appeared to be derived directly from the infiltrating duct carcinoma as the result of invasion of the epidermis, and the location on the arm is unique since no mammary or sweat glands are present to the extent they are in the breast, axilla, or anogenital areas, where Paget's disease has most commonly occurred.
Greenwood SM, Minkowitz S. Paget's Disease in Metastatic Breast Carcinoma. Arch Dermatol. 1971;104(3):312-315. doi:10.1001/archderm.1971.04000210086017