Metastatic ductal eccrine adenocarcinoma masquerading as an invasive ductal carcinoma of the male breast.

We report the case of a 38-year-old man with metastatic ductal eccrine adenocarcinoma (DEA) of the left breast responding to 5-flourouracil, epirubicin and cyclophosphamide (FEC) chemotherapy. He initially presented with a 2-week history of difficulty walking because of bilateral hip and lower back pain. Examination showed an ulcerating cutaneous mass over the left anterior chest wall, left axillary lymphadenopathy and tenderness over the spine. A punch biopsy of the breast lesion resulted in a diagnosis of metastatic invasive ductal carcinoma (IDC) of the breast. He received palliative radiotherapy to the spine and also received six cycles of FEC chemotherapy and was subsequently commenced on tamoxifen and ibandronate. There was a symptomatic and radiological response to the FEC chemotherapy. Referral was subsequently made to our institution where the original punch biopsy was reviewed. This showed tumor cells that were polygonal with darkly stained pleomorphic nuclei and abundant eosinophilic cytoplasm and were also localized to areas of fibrotic stroma containing eccrine glands and ducts but did not appear to involve mammary tissue. Immunohistochemical studies showed the tumors to be cytokeratin 7 and gross cystic disease fluid protein-15/ prolactin inducible protein negative and estrogen receptor alpha positive. Both the morphological and the immunohistochemical characteristics of the tumor were consistent with a revised diagnosis of DEA rather than IDC. When last reviewed, the patient remains pain free and his disease stable 17 months after his original presentation. This case emphasizes the challenge in discriminating histopathologically between two rare tumors of the male breast, namely DEA and IDC. In addition, clinical response to FEC by metastatic DEA has not been previously documented, and this therapeutic regimen warrants further investigation.