Abstract

Myoepithelial carcinoma is a rare malignant neoplasm comprised of a pure population of atypical myoepithelial cells. We present a case of a 45-year-old woman with a 3.0 cm, erythematous, ulcerated lesion on the chest wall. The excisional specimen showed a 3.1 cm tumor with a homogeneous, white, firm cut surface and a maximum tumor depth of 1.0 cm. Histologic examination revealed an ulcerated, circumscribed, cellular, dermal-based tumor broadly abutting the subcutaneous fat. Epidermal involvement was not appreciated. The lesion was comprised of markedly pleomorphic epithelioid cells growing in sheets and vague fascicles, set within a myxoid stroma. The cells were characterized by round to ovoid, eccentrically-placed vesicular nuclei, macronucleoli, and abundant amphophilic cytoplasm. Scattered nuclear pseudoinclusions were present. Mitotic activity was increased and lymphovascular invasion was identified. Necrosis was not readily appreciated. The tumor cells showed immunoreactivity for S100, SOX10, calponin, and p63, consistent with a diagnosis of myoepithelial carcinoma. Pan-keratin highlighted scattered lesional cells. Melan-A, HMB-45, and CD34 were negative. While the clinical history and histologic findings in this case were all highly suspicious for melanoma, it distinctly lacked an in-situ component. This case emphasizes the importance of critical appraisal of any primary cutaneous melanoma that lacks epidermal involvement because it just might be a myoepithelial carcinoma! In addition, myoepithelial carcinoma should be included in the differential for malignant S100/SOX-10 positive tumors and additional stains should be performed to rule out this diagnosis.

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