Pseudovascular adenoid squamous cell carcinoma of the lung: clinicopathologic study of three cases and comparison with true pleuropulmonary angiosarcoma.

Pseudovascular adenoid squamous cell carcinoma (PASCC) is a variant epithelial neoplasm with the ability to simulate the growth pattern of angiosarcoma. It has been documented in the breast, skin, and, recently, lung. We describe three additional examples of pulmonary PASCC occurring in two men and one woman. The patients' ages ranged from 47 to 54 years at diagnosis, and all patients had radiographically and macroscopically typical squamous carcinomas of the lung. Histologically, the tumors showed the presence of interanastomosing pseudoluminal spaces that were lined by obviously atypical epithelioid cells and focally contained erythrocytes. Overtly carcinomatous growth was apparent only very focally. A comparison case of true pleuropulmonary angiosarcoma in a 57-year-old man showed closely similar microscopic features, but it lacked areas that resembled conventional carcinomas. Immunohistologic studies revealed uniform reactivity for keratin in PASCC of the lung. Two cases also stained positively for epithelial membrane antigen and vimentin, but all of them were negative for von Willebrand factor, CD31, CD34, and binding of Ulex europaeus I lectin. Electron microscopic examination of the three cases showed the presence of intercellular desmosomes and cytoplasmic tonofibrils. The example of true pleuropulmonary angiosarcoma demonstrated an endothelial immunophenotype. Two of three patients with pulmonary PASCC survived for at least 20 months, whereas the individual with true angiosarcoma died within 3 months. Together with prior reports on such lesions, these data suggest that angiosarcoma-like carcinomas of the lung differ pathologically and behaviorally from primary pulmonary endothelial malignancies.