Squamoid Eccrine Ductal Carcinoma

Summary: Squamoid eccrine ductal carcinoma is an exceedingly rare tumor, often affecting sun exposed skin of the head and neck individuals in the 7th to 8th decades. It can be associated with immunosuppression in solid organ transplant recipients. Clinically and histologically, it can mimic squamous cell carcinoma. We present a case of a 73-year-old man with a several week history of a crusted papule on the right side of his nose. His past medical history is notable for history of heart failure requiring cardiac transplantation in 2013, on multiple immunosuppressive medications since that time, including everolimus and tacrolimus at the time of presentation. In the 2-3 years prior to presentation the patient had been undergoing treatment for multiple squamous cell carcinomas on the trunk, face and extremities. Punch biopsy of the lesion of concern to the right nose demonstrated an atypical squamous proliferation, with ulceration, and areas of squamous eddies and keratin cyst formation superficially, with cords and strands of cells extending into the deep dermis. At higher magnification in the deep dermis marked pleomorphism and atypia was observed, as well atypical ductal differentiation in a background desmoplastic stroma. Immunohistochemistry stains of the cells of interest for p63, cytokeratin 5/6 (CK5/6), CEA, and EMA are performed and support a diagnosis of squamoid eccrine ductal carcinoma.