Pseudovascular adenoid squamous cell carcinoma of the skin. A neoplasm that may be mistaken for angiosarcoma.

The adenoid variant of squamous cell carcinoma has been well-documented in several anatomic sites, including the skin. This tumor is characterized by acantholytic arrays of neoplastic keratinocytes that form pseudoglandular profiles. Although it is typically confused with adenocarcinomas, adenoid squamous cell carcinoma also may be mistaken for malignant vascular proliferations. This report concerns six acantholytic cutaneous squamous cell carcinomas that closely simulated angiosarcomas on conventional histologic examination. They arose in sun-exposed skin areas in middle-aged or elderly patients (mean age, 60 years), five of whom were men. In contrast to the typical clinical appearance of angiosarcoma, pseudovascular adenoid squamous cell carcinoma presented itself as a discrete cutaneous ulcer or crusted tanpink nodule. Microscopically, this lesion was characterized by interanastomosing cordlike arrays of polygonal or flattened tumor cells, with internal pseudolumina that contained detached tumor cells. A connection between the dermal neoplasm and the epidermis was apparent in three cases, but it was focal. Erythrocytes were seen in pseudovascular spaces in five tumors. Immunohistochemically, all examples of pseudovascular adenoid squamous carcinoma were reactive with antibodies to cytokeratin and epithelial membrane antigen (EMA). In addition, three expressed vimentin, two exhibited blood group antigen-positivity, and two bound Ulex europaeus I agglutinin. None of them was immunoreactive for Factor VIII-related antigen, and two of three studied for CD34-reactivity were likewise negative. A control group of six cutaneous angiosarcomas was uniformly nonreactive for cytokeratin and EMA, but they showed positivity for vimentin, Ulex binding, and CD34 positivity in all instances. Pseudovascular adenoid squamous cell carcinoma may be distinguished effectively from angiosarcoma of the skin by attention to its clinical features and by appropriate immunohistochemical studies. These two tumors differ in biologic behavior; three patients with pseudovascular adenoid squamous cell carcinoma died of their tumors, whereas all angiosarcomas in this series proved fatal.