Apocrine gland carcinoma of the mammary skin concomitant with pagetoid phenomenon

We reported a 52‐year‐old woman with an apocrine gland carcinoma of the mammary skin concomitant with pagetoid phenomenon. She had a 23‐year history of a small nodular lesion on the lower left part of her right breast with a 1‐year history of the pigmented plaque spreading peripherally around the nodule. Our diagnosis revealed that the nodule was an apocrine gland carcinoma and the intraepidermal neoplastic cells with pagetoid spread in the pigmented plaque were derived from the apocrine gland carcinoma. No Paget’s cells were detected in the right nipple, and no tumor cells were observed in the sentinel lymph node and underlying mammary gland tissue. We also investigated the immunohistochemical changes in this case. They showed that both intraepidermal neoplastic cells with pagetoid spread and tumor cells of the apocrine gland carcinoma were positive with cytokeratin‐7 and human epidermal growth factor receptor‐2 (HER‐2)/neu overexpression. The results of the present study conclude that the intraepithelial spread of tumor cells in the mammary skin distant from the nipple occurred as a pagetoid phenomenon, and that HER‐2 may have a key role in pagetoid phenomenon of an underlying apocrine gland carcinoma, as well as in mammary Paget’s disease.