Unusual primary lung neoplasms: spindle cell and undifferentiated lung carcinomas expressing only vimentin

Two unusual primary carcinomas of the lung are described. One occurred in a 31-year-old man and was composed of large, undifferentiated, ovoid to polygonal cells. The other occurred in a 72-year-old man, was composed of spindle-shaped cells, and was initially diagnosed as a localized fibrous mesothelioma. The neoplastic cells of these tumors expressed only vimentin intermediate filaments and showed no other immunohistochemical features of epithelial neoplasms, although they exhibited a metastatic pattern characteristic of lung carcinomas. These two malignant neoplasms further expand the spectrum of unusual lung neoplasms, and suggest that there are pulmonary carcinomas that contain only vimentin intermediate filaments.