Abstract

Cutaneous metastases of breast carcinoma are common and must be distinguished from a wide variety of other neoplasms. We report the case of a 75-year-old woman who presented to dermatology clinic with growing erythematous, well-defined, indurated nodules on the left chest, right shoulder, and left posterior arm. The lesions were asymptomatic, and review of systems was otherwise negative. Biopsy of the right shoulder nodule revealed skin with unremarkable epidermis and dermal involvement by cohesive clusters of malignant epithelioid cells arranged in nests and cords with rudimentary gland formation. Lesional cells displayed nuclear contour irregularity and prominent nucleoli, and a minor subset had indented nuclei with vacuolated cytoplasm. No epidermal involvement by lesional cells was noted. Tumor cells were positive for adipophilin, androgen receptor, and EMA. BerEp4 was focally positive. The tumor cells showed retained expression of DNA mismatch repair proteins. It was further elucidated that the patient had a remote history of breast cancer with metastases to bone. Additional immunohistochemical workup revealed lesional cells were diffusely positive for ER and PR, and HER2 exhibited dim positivity in a minor subset (2+). CK7 showed patchy positivity. The immunomorphologic findings in this case were compatible with cutaneous metastasis of breast carcinoma with sebaceous differentiation. Breast cancer with sebaceous differentiation is exceptionally rare, and to our knowledge, cutaneous metastasis of such a tumor has only been reported once previously. In this case, the focal sebaceous differentiation and immunohistochemical expression of adipophilin and androgen receptor raised the possibility of sebaceous carcinoma; however, the clinical history, lack of an epidermal connection, and other immunohistochemical results led to the correct diagnosis. This case demonstrates a potential pitfall in the diagnosis of sebaceous neoplasms in the skin.

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