Squamoid Eccrine Ductal Carcinoma: A Clinicopathologic Study of 30 Cases.

Squamoid eccrine ductal carcinoma is a poorly documented skin adnexal carcinoma showing squamous and duct differentiation. It is regarded to be of low-grade malignant potential, but limited follow-up information is available. To study their clinical behavior and histologic features, 30 squamoid eccrine ductal carcinomas were identified from departmental and referral files. Hematoxylin and eosin-stained sections were reviewed, and immunohistochemistry for carcinoembryonic antigen and epithelial membrane antigen was examined to confirm duct differentiation. Clinical follow-up was obtained from patient records and referring pathologists. The tumors presented as nodules or plaques (median size, 1.0 cm; range, 0.5 to 2.5 cm) with a predilection for the head and neck (77%). The patients were elderly (median age, 79.5 y; range, 10 to 96 y) with a male predominance. Histologically, these poorly demarcated tumors were characterized by an infiltrative growth pattern within the dermis and additional invasion of subcutis in 70%. Median tumor thickness was 4.3 mm (range, 1.5 to 18 mm). Superficially, the tumors resembled well-differentiated squamous cell carcinoma. In the deeper reaches, they were organized in cords and strands showing duct differentiation in a desmoplastic stroma. Cytologic atypia was moderate to severe. Ulceration (47%), necrosis (23%), and perineural and lymphovascular infiltration (27% and 6%, respectively) were additional features. Follow-up data (median, 29 mo; range, 7 to 99), available for 24 patients (80%), revealed a local recurrence rate of 25%. Three patients had lymph node metastasis, and 1 patient died of metastatic disease. Our study outlines the histologic characteristics of squamoid eccrine carcinoma and emphasizes its clinical behavior with risk for local recurrence and potential for more aggressive behavior with metastasis and rare disease-related mortality.