Abstract
We present the case of a 77 y.o. Egyptian female with a five year history of a growing 2.5 x 7.5 cm right parietal scalp tumor. Biopsy of the tumor by her local dermatologist was consistent with microcystic adnexal carcinoma. She underwent standard excision which yielded grossly positive margins. To remove the residual tumor, she was referred to a tertiary-care-center for Mohs Micrographic Surgery. Tumor margins were cleared after five Mohs layers. Histologic sections revealed irregular islands and strands of tumor with prominent squamous differentiation, squamous pearl formation, and irregular eccrine structures. Overall, these findings were most consistent with squamoid eccrine ductal carcinoma. Closure of the defect was completed with an anterolateral thigh free flap and split-thickness skin graft from the right thigh. Squamoid eccrine ductal carcinoma (SEDC) is an exceedingly rare, malignant eccrine carcinoma of squamous and ductal differentiation. Histology classically exhibits prominent squamous proliferation with atypia, keratinous cyst formation, squamous eddies, and eccrine ductal differentiation. Morphologically, SEDC may resemble squamous cell carcinoma or other eccrine carcinomas such as microcystic adnexal carcinoma. The diagnosis of SEDC is challenging due to its rarity and superficiality of many biopsies. In our case, the presence of a squamous component distinguished this entity from microcystic adnexal carcinoma. Differentiation between SEDC and other eccrine carcinomas is important for proper management and treatment. SEDC has demonstrated more aggressive local behavior, with a pattern of deep infiltrative growth, perineural and intravascular invasion, as well as potential for recurrence or metastasis. Traditionally, eccrine carcinomas are treated with wide local excision. However, Mohs Micrographic Surgery has been shown to decrease recurrence rates when compared to conventional surgical excision for treatment of eccrine carcinomas.
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