Abstract

Sarcomatoid carcinoma (SC) has histologic features reminiscent of sarcoma yet retains immunohistochemical evidence of epithelial differentiation. The majority of cutaneous SC are sarcomatoid squamous cell carcinoma.  SC may show a transition between the epithelial component or be entirely sarcomatoid histologically. Carcinosarcoma is defined as an abrupt transition from a carcinoma component to a sarcoma component that lacks evidence of epithelial differentiation. We present the case of an 88-year-old patient with a 1.8 cm exophytic, friable, and erythematous nodule on the right infra-auricular neck. The histologic sections demonstrated an infiltrative triphasic malignant neoplasm. The tumor had squamous differentiation with involvement of the epidermis (squamous cell carcinoma in situ) that transitioned to infiltrative cords and islands forming glandular structures compatible with squamoid eccrine ductal carcinoma. There was an abrupt transition from the squamoid eccrine ductal carcinoma into malignant spindled cell population arranged in long intersecting fascicles. Both components had enlarged nuclei, vesicular chromatin, prominent nucleoli and abundant eosinophilic cytoplasm.  Multiple mitotic figures including atypical forms were identified. CK7, AE 1/3, and CK5/6 stains were positive both in the epithelial and sarcomatoid areas. A CEA stain revealed focal ductal lumens in the epithelial cords and islands, and the p63 stain highlighted a peripheral myoepithelial layer in the ductal component.  The SOX10, CK20, and S100 stains were negative. Based on the findings, a diagnosis of sarcomatoid squamoid eccrine ductal carcinoma was rendered. To the best of our knowledge, this is the first such case to be reported in the English literature.