Abstract

Introduction: Merkel cell carcinoma (MCC) is a rare tumor of skin which when occurs in the breast should be differentiated from primary mammary tumors including Merkel cell-like carcinoma of the breast. Merkel cell carcinoma of the mammary skin is an aggressive cutaneous neoplasm, second in that regard only to melanoma. The face and extremities are the most common locations. We present a case of primary MCC in a male patient. Case Synopsis: A 64 years old man who had kidney transplantation 15 years ago and under immunosuppressive therapy, came with multiple purple papular and plaque-like non painful skin lesions on right nipple, areola and breast skin (figure A). Cytology showed malignant small round cell tumor (figure B). Skin biopsy was performed that revealed undifferentiated malignant small tumor cells(Figure C) which were positive for cytokeratin 20 (Figure D), pancytokeratin (dot-like pattern)(figure D inset), CD56, NSE, chromogranin A and EMA and negative for estrogen and progesterone receptors, PSA, leukocyte common antigen,thyroid transcription factor 1(TTF-1), cytokeratin 7 and S100 . Consequently the diagnosis of merkel cell carcinoma was confirmed and modified radical mastectomy with axillary fat pad and lymph node resection were performed(figure G). All of the 24 submitted lymph nodes were involved by tumor cells. Conclusion: MCC can mimic breast parenchymal neoplasms clinically and pathologically.The differential diagnoses of MCC are poorly differentiated neuroendocrine carcinoma of breast, lymphomas, certain sarcomas and small cell carcinomas especially metastasis from lung origin. Dermatologists and surgical oncologists should consider dermal mimickers of breast primaries in approaching any breast mass.

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